Light Scattering Type Smoke Detector

ABSTRACT

A light scattering type smoke sensor includes a sensor body, light-emitter for emitting light toward an open smoke-sensing space and outputting a light-received signal according to the amount of scattering light received, and a fire judging unit for judging whether fire occurs or not on the basis of the amount of received light determined on the basis of the outputted light-received signal.

TECHNICAL FIELD

The present invention relates to a light scattering type smoke sensorwhich senses smoke by emitting light and detecting light scattered bythe smoke.

BACKGROUND ART

A conventional light scattering type smoke sensor basically includes asmoke chamber through which smoke enters into the sensor from outside.An inside space of the smoke chamber functions as a smoke-sensing space,in which light emitted by a light-emitting element is scattered bysmoke, and scattered light is received by a light-receiving element sothat occurrence of fire can be detected.

The smoke-sensing space is provided inside the smoke chamber of thesensor in order to realize an accurate sensing of minute scatteringlight generated by reflection of light by the smoke without beingaffected by outside light, and also to prevent entrance of foreignsubstances into the smoke-sensing space. Presence of foreign substancessuch as a small insect in the smoke-sensing space may cause scatteringof light and lead to false alarm. Therefore, the arrangement of thesmoke-sensing space inside the smoke chamber is an essential part of theconventional light scattering type smoke sensor (see, for example,Patent Document 1 and Patent Document 2).

Patent Document 1: Japanese Patent Application Laid-Open No. H6-109631Publication

Patent Document 2: Japanese Patent Application Laid-Open No. H7-12724Publication

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In the conventional light scattering type smoke sensor, however, thefact that the smoke chamber is a necessary structural element createsproblems.

Firstly, in the conventional smoke sensor, a portion where the smokechamber is arranged protrudes outwards so as to facilitate inflow of thesmoke into the smoke chamber. When such a smoke sensor is arranged on aceiling surface or the like, the portion sticks out from the ceilingsurface which is visually undesirable when interior design isconsidered.

Further, since the smoke coming into the smoke chamber from outsidepasses through elements arranged around the smoke chamber, such as acover, a smoke inlet, an insect screen, and a labyrinth for shieldingoutside light (light shielding wall), a desirable characteristic ofsmoke inflow cannot be obtained, and the sensing of smoke may delay.

Furthermore, when dusts or the like adhere or dew forms inside the smokechamber while the smoke sensor is in an installed state, signal to noiseratio (S/N) may be deteriorated or false alarm may occur due to lightreflected inside the smoke chamber. Hence, the smoke chamber needs to becleaned and checked periodically, whereby maintenance cost increases.

If it is possible to eliminate the influence of outside light on thescattering light generated by smoke utilizing the characteristics oflight wavelength or the polarization characteristics, the smoke chamberis not necessary for the formation of the smoke-sensing space inside thesmoke sensor. Such solution is advantageous in various points, forexample, in that it can eliminate inconveniences of the conventionalsmoke chamber.

In view of the above, an object of the present invention is to provide asmoke sensor which utilizes scattering light and which does not need asmoke chamber inside.

Mean(s) for Solving the Problems

In order to solve the problems as described above and to achieve anobject, the present invention of claim 1 includes, a sensor body; alight-emitter that is incorporated in the sensor body to emit lighttoward an open smoke-sensing space located outside the sensor body; alight-receiver that is incorporated in the sensor body to receivescattered light generated by the light emitted from the light-emitter tothe smoke-sensing space, and to output a light-received signalcorresponding to an amount of received light scattered; and a firejudging unit that judges presence/absence of fire occurrence based onthe amount of received light identified by the light-received signaloutput from the light-receiver.

The present invention of claim 2 according to claim 1, wherein the firejudging unit judges the present/absence of the fire occurrence based onthe amount of received light and a differential value of the amount ofreceived light.

The present invention of claim 3 according to claim 2, wherein the firejudging unit judges that fire occurs when the amount of received lightexceeds a predetermined fire threshold and the differential value of theamount of received light is equal to or lower than a predetermined falsealarm threshold.

The present invention of claim 4 according to claim 3, wherein when theamount of received light exceeds the predetermined fire threshold, andthe differential value of the amount of received light exceeds thepredetermined false alarm threshold, the fire judging unit checkswhether the amount of received light exceeds a predetermined obstaclethreshold or not when a predetermined time elapses since the time thedifferential value exceeds the predetermined false alarm threshold, andjudges that there is an obstacle for fire sensing when the amount ofreceived light exceeds the obstacle threshold.

The present invention of claim 5 according to claim 1, wherein the firejudging unit judges that fire occurs, when the amount of received lightexceeds a predetermined first fire threshold for a time equal to orlonger than a predetermined first set time, and the amount of receivedlight exceeds a predetermined second fire threshold which is higher thanthe first fire threshold for a time equal to or longer than apredetermined second set time which is longer than the first set time.

The present invention of claim 6 according to any one of claims 1 to 5,wherein the light-emitter has plural light-emitters.

The present invention of claim 7 according to claim 6, wherein thelight-emitter has first light-emitter that emits light of a firstwavelength, and second light-emitter that emits light of a secondwavelength which is shorter than the first wavelength, and a firstscattering angle formed by mutual crossing of a light axis of the firstlight-emitter and a light axis of the light-receiving element is smallerthan a second scattering angle formed by mutual crossing of a light axisof the second light-emitter and the light axis of the light-receivingelement.

The present invention of claim 8 according to claim 7, wherein a centralwavelength of the first wavelength is equal to or longer than 800 nm, acentral wavelength of the second wavelength is equal to or shorter than500 nm, the first scattering angle falls within a range of 20° to 50°,and the second-scattering angle falls within a range of 100° to 150°.

The present invention of claim 9 according to claim 6, wherein thelight-emitter has first light-emitter and second light-emitter, thefirst light-emitter emits light having a polarization plane vertical toa first scattering plane that passes through a light axis of the firstlight-emitter and a light axis of the light-receiving element, thesecond light-emitter emits light having a polarization plane parallel toa second scattering plane that passes through a light axis of the secondlight-emitter and the light axis of the light-receiving element, and afirst scattering angle formed by mutual crossing of the light axis ofthe first light-emitter and the light axis of the light-receivingelement is smaller than a second scattering angle formed by mutualcrossing of the light axis of the second light-emitter and the lightaxis of the light-receiving element

The present invention of claim 10 according to claim 9, wherein thefirst scattering angle is equal to or smaller than 80°, and the secondscattering angle is equal to or larger than 100°.

The present invention of claim 11 according to any one of claims 6 to10, wherein the plural light-emitters are arranged at solid angles, sothat planes including respective light axes of the plural light-emittersand the light axis of the light-receiving element are substantially notidentical with each other.

The present invention of claim 12 according to any one of claims 6 to11, wherein the light-emitter includes first light-emitter and secondlight-emitter, the fire judging unit compares an amount of receivedlight by the light-receiver with respect to scattered light generatedfrom the light emitted by the first light-emitter and scattered bysmoke, and an amount of received light by the light-receiver withrespect to scattered light generated from the light emitted by thesecond light-emitter and scattered by the smoke, to identify a type ofthe smoke, and judges the presence/absence of fire occurrence based on astandard corresponding to the type of the smoke.

The present invention of claim 13 according to any one of claims 1 to12, wherein a mutual crossing point of the light axis of thelight-emitter and the light axis of the light-receiver in thesmoke-sensing space is at least approximately 5 mm away from the sensorbody.

The present invention of claim 14 according to any one of claims 1 to13, wherein at least one portion of an outer surface of the sensor bodyis configured by an insect avoiding material, or an insect avoidingagent is applied or made to permeate to at least one portion of theouter surface of the sensor body.

The present invention of claim 15 according to any one of claims 1 to14, wherein the light-receiver has an angle of field of view not largerthan 5 degrees.

The present invention of claim 16 according to any one of claims 1 to15, wherein the light-emitter emits collimated parallel beam.

The present invention of claim 17 according to any one of claims 1 to16, further including a logarithmic amplifier which amplifies thelight-received signal output from the light-receiver.

The present invention of claim 18 according to any one of claims 1 to17, further including a light emission controller that drives thelight-emitter to intermittently emit light by using a modulatedlight-emission signal, and an amplifier that amplifies thelight-received signal output from the light-receiver in synchronizationwith the modulated light-emission signal.

The present invention of claim 19 according to claim 18, furtherincluding a light emission controller that drives the light-emitter tointermittently emit light by using a modulated light-emission signal,wherein the light-emitter emits light within a visible light wavelengthband, and the light emission controller drives to intermittently emitlight at a light-emission pulse width of equal to or smaller than 1millisecond.

The present invention of claim 20 according to claim 19, wherein thelight emission controller sets a total light emission time period in anintermittent light emission equal to or smaller than 1 millisecond.

EFFECT OF THE INVENTION

According to the present invention, since light is emitted towards thesmoke-sensing space outside the sensor body and received therefrom, thesmoke-sensing point can be set outside the sensor body for smokesensing. Therefore, the smoke chamber is not necessary, and theconventional structure in which the portion of the smoke chamberprotrudes is not necessary, and the portion corresponding to the smokechamber can be made flat and thin. As a result, when the lightscattering type smoke sensor is installed on a ceiling surface, an outersurface of the sensor body which is located at a side of thesmoke-sensing space can be made substantially coplanar to the ceilingsurface, whereby a full-flat installation, i.e., an installation whichdoes not make the sensor stick out from the ceiling surface, can berealized. Further, since the ceiling surface can be designed andconstructed as a full-flat ceiling, the quality of interior design canbe greatly improved. Still further, since the light scattered by thesmoke is detected in the open space outside the outer surface of thesensor and the open outside space serves as the smoke-sensing space,there is no structural element that prevents the inflow of smokedissimilar to the conventional smoke chamber. Hence, the smoke of thefire can be detected without delay. Still further, since the openoutside space serves as the smoke-sensing space and the outer surface ofthe sensor body facing the open smoke-sensing space is exposed to theoutside space below, no dust adhere to or dew forms on the surface.Therefore, the false alarm is not caused by such foreign substances, andno cleaning is required, whereby the maintenance cost can be reduced.

Further, according to the present invention, since fire judgment isperformed based on the amount of received light and the differentialvalue thereof, even when the insect or other foreign substances exist inthe smoke-sensing space, false alarm can be prevented, whereby problemscaused by the use of the open space as the smoke-sensing space can beeliminated.

Still further, according to the present invention, the smoke sensordecides that the fire occurs when the amount of received light exceedsthe predetermined fire threshold, and the differential value of theamount of received light is not higher than the predetermined falsealarm threshold. Since the increase in the smoke concentration caused bythe fire proceeds moderately compared with the change in the amount ofreceived light caused by foreign substances such as insects, the smokesensor does not decide that the fire occurs even when the amount ofreceived light reaches the level of the fire, and decides that the fireoccurs only after the differential value thereof is confirmed to beequal to or less than the abnormal threshold. Thus, even when theforeign substances such as an insect exist in the smoke-sensing space,the false alarm of the smoke sensor can be prevented even moreassuredly.

Still further, according to the present invention, when the amount ofreceived light exceeds the predetermined obstacle threshold after thepredetermined time elapses since the differential value exceeds thepredetermined false alarm threshold, the smoke sensor decides that theforeign substance creates obstacle for sensing. The changes in thelight-received signal caused by the foreign substances such as insectcan be classified into a temporal change and a continuous change.Abnormal change in the light-received signal caused by incoming insectsor the like is temporal and the light-received signal returns to anormal state after a certain time elapses since the differential valuethereof exceeds the abnormal threshold value. Hence, if thelight-received signal returns to a level equal to or lower than theobstacle threshold after a certain time, the cause of such changes canbe decided as non-obstacle. On the other hand, when a spider's nest,curtain, or the like moves into or contacts with the smoke-sensingspace, the light-received signal remains at the abnormal level over theobstacle threshold even after the certain time period elapses. In suchcase, the smoke sensor is in a troubled state where the smoke sensorcannot properly sense the smoke. When the smoke sensor is in such state,the smoke sensor regards such state as the obstacle and makesnotification, whereby the maintenance check of the smoke sensor can berealized.

Still further, according to the present invention, when the amount ofreceived light remains to be over the first fire threshold for a timeperiod equal to or longer than the first set time, and when the amountof received light remains to be over the second fire threshold for atime period equal to or longer than the second set time, the smokesensor decides that the fire occurs. In the conventional lightscattering type smoke sensor and including the smoke chamber, it isdifficult to distinguish the changes in smoke concentration of the smokeof the fire from the changes in smoke concentration of smoke cause byother reasons than fire (such as tobacco, or cooking), since the changestend to be similar. Contrarily, the light scattering type smoke sensorof the present invention which does not need the smoke chamber has acharacteristic that the different characteristics of the smoke of fireand the smoke caused by other reasons can be directly reflected in thesensing results. Thus, the smoke sensor of the present inventiondistinguishes two different types of smokes and prevents the falsealarm.

Still further, according to the present invention, since the smokesensor has plural light-emitters, the smoke sensor of the presentinvention can make multiple decision based on the plural data on theamounts of received light, whereby the decision on the occurrence offire can be even more precisely made.

Still further, according to the present invention, two light-emitteremit light at different scattering angles to the light-receivingelement. Hence, the light scattering characteristic of the smoke is madedifferent for each type of the smoke. At the same time, twolight-emitting units emit light of different wavelengths. Hence, thelight scattering characteristic of the smoke is made different for eachtype of the smoke due to the light wavelengths. The combined effect ofthe differences in the light scattering angles and the light wavelengthscreates a significant difference in scattering light intensity dependingon the types of the smoke. Thus, the different types of smoke can bedistinguished more accurately. Even though the smoke-sensing space isoutside, the sensing of the smoke of fire can be accurately performedwithout being affected by the outside light. Further, alarm would not beraised by non-fire such as steam generated by cooking or smoke oftobacco. Still further, the smoke of fire can be distinguished based onthe types of combusted materials, and the types of fire, such as blacksmoke fire and white smoke fire can be accurately distinguished.

Still further, according to the present invention, two light-emittingunits have different polarization planes for each scattering plane ofthe light emitted therefrom. Hence, the light scattering characteristicscan be made different according to the polarization directions of light.At the same time, since two light-emitting units have differentscattering angles for the light-receiving element, light scatteringcharacteristics can be made different depending on the types of smoke.The combined effect of the differences in the light polarizationdirections and the light scattering angles creates a significantdifference in scattering light intensity depending on the types ofsmoke. Thus, the types of smoke can be distinguished more accurately.Even though the smoke-sensing space is in outside, the sensing of thesmoke of fire can be accurately performed without being affected by theoutside light. Further, alarm would not be raised by non-fire such assteam generated by cooking or smoke of tobacco. Still further, the smokeof fire such as black smoke fire and white smoke fire can bedistinguished, and the types of combusted materials can be accuratelydistinguished.

Still further, according to the present invention, since the plurallight-emitters are arranged at solid angles, the smoke-sensing point,which is a crossing point of the light axis of the light-emitter and thelight axis of the light-receiver, can be arranged in a space outside theouter surface of the sensor body for the sensing of scattering lightgenerated by the smoke.

Still further, according to the present invention, the amount ofreceived scattering light generated by the light emitted from the firstlight-emitter is compared with the amount of received scattering lightgenerated by the light emitted from the second light-emitter. Forexample, the ratio of the two is calculated and compared with thethreshold. Based on the comparison, the type of the smoke isdistinguished and the fire judgment is performed based on a differentstandard according to the type of smoke. Such multiple decision makingbased on the plural data of the amount of received light allows forstill more accurate fire sensing.

Still further, according to the present invention, the crossing point ofthe light axis of the light-emitter and the light axis of thelight-receiver is set at a point away from the sensor body by a distanceequal to or longer than 5 mm. Hence, even when the dust adheres to theouter surface of the sensor body or an insect wriggles on the outersurface of the sensor body, such foreign substances do not affect thesensing.

Still further, according to the present invention, at least one portionof the outer surface of the sensor body is formed from an insectavoiding material or the like. Hence, the insects rarely approach theouter surface and the false alarm can be prevented in advance.

Still further, according to the present invention, the angle of field ofview of the light-receiving unit is set equal to or narrower than 5degrees. Thus, the size of the area for scattering light sensing can beset to a requisite minimum in the smoke-sensing space, and the influenceof the outside light can be prevented.

Still further, according to the present invention, the light-emitteremits collimated parallel beam. Hence, the size of the area for thescattering light sensing can be set to a requisite minimum in thesmoke-sensing space, and the influence of the outside light can beprevented.

Still further, according to the present invention, the light-receivedsignal is amplified by a logarithmic amplifier. Hence, even when theoutside light directly comes into the light-receiving element so that anormal linear amplifier undergoes output saturation so as to lose thefunction of amplification, the logarithmic amplifier does not undergooutput saturation of received light so as to fail the amplification,whereby stable fire sensing can be allowed.

Still further, according to the present invention, the light-emitter isdriven to intermittently emit light by a modulated light-emissionsignal, and the light-received signal is amplified in synchronizationwith the modulated light-emission signal. The modulated light emissionand the synchronous light-received allow for the elimination ofillumination light or the like which causes false alarm from a target ofsensing, whereby the false alarm can be surely prevented from beingcaused by the outside light.

Still further, according to the present invention, since thelight-emission pulse width is set equal to or smaller than 1millisecond, the time period of light emission is not sufficient for thehuman visual sensitivity, whereby the human cannot recognize theblinking of the light-emitting unit of the smoke sensor.

Still further, according to the present invention, the total time periodof light emission by the intermittent light emission driving is set to alength equal to or shorter than 1 millisecond. Hence, the light emissiontime period can be set so that the light is inperceptible for the humanvisual sensitivity, whereby the human cannot recognize the blinking ofthe light-emitting unit of the smoke sensor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a light scattering type smoke sensoraccording to a first embodiment;

FIG. 2A shows the light scattering type smoke sensor according to thefirst embodiment installed on a ceiling surface;

FIG. 2B shows the light scattering type smoke sensor according to thefirst embodiment embedded and installed in the ceiling surface;

FIG. 3 is a perspective view of a chamber base;

FIG. 4 is a sectional view of an entire smoke-sensing unit including thechamber base of FIG. 3;

FIG. 5 is a circuit block diagram of the light scattering type smokesensor according to the first embodiment;

FIG. 6 is a time chart of driving for light emission by a light emissioncontrolling unit of FIG. 5;

FIG. 7 is a circuit block diagram of a hardware in which a function of afire judging unit in a signal processing unit of FIG. 5 is realized;

FIG. 8 is a time chart of an operation of the fire judging unit of FIG.7 when the smoke sensor receives smoke of fire;

FIG. 9 is a time chart of a temporal increase in scattering light;

FIG. 10 is a time chart obtained when a foreign substance adheres to anouter surface of a sensor body near smoke-sensing point P;

FIG. 11 is a flowchart of a process for executing the function of thefire judging unit in the signal processing unit of FIG. 5 throughprogrammed control;

FIG. 12 is a perspective view of a chamber base of a light scatteringtype smoke sensor according to a second embodiment;

FIG. 13A is a schematic representation in three-dimensional coordinatespace of an optical positional relation corresponding to positions of alight-emitting unit and a light-receiving unit in the chamber base ofFIG. 12;

FIG. 13B is a diagram of a light axis of light emission and a light axisof light-received in a horizontal x-y plane;

FIG. 14 shows a relation between scattering light angle and amount ofscattering light for different types of smoke;

FIG. 15 shows a relation between scattering angle and ratio of amount ofscattering light of kerosene combustion smoke/cotton lampwick fumigationsmoke to filter paper fumigation smoke;

FIG. 16 is a sectional view of a light scattering type smoke sensoraccording to a third embodiment;

FIG. 17 is a perspective view of a chamber base;

FIG. 18 is a sectional view of an entire smoke-sensing unit includingthe chamber base of FIG. 17;

FIG. 19 is a circuit block diagram of the light scattering type smokesensor according to the third embodiment;

FIG. 20A shows a solid-angle arrangement of light axes of a firstlight-emitting element, a second light-emitting element, and alight-receiving element;

FIG. 20B shows the solid-angle arrangement of point A of the firstlight-emitting element and point C of the light-receiving element;

FIG. 20C shows the solid-angle arrangement of point B of the secondlight-emitting element and point C of the light-receiving element;

FIG. 21 shows relation of locations of the first light-emitting element,the second light-emitting element, and the light-receiving element whenthe light axes thereof are assumed to be on a same plane;

FIG. 22 shows a relation between angle of field of view and area offield of view;

FIG. 23 is a graph of scattering efficiency I against scattering angle θfor fumigation smoke generated by combustion of the cotton lampwick;

FIG. 24 is a graph of scattering efficiency I against scattering angle θfor combustion smoke generated by combustion of kerosene;

FIG. 25 shows amounts of light-received signals and ratio thereof forthe fumigation smoke of the cotton lampwick and the combustion smoke ofkerosene;

FIG. 26 is a flowchart of a fire sensing process performed in thecircuit block of FIG. 19;

FIG. 27 is a flowchart of an obstacle judgment process of FIG. 26;

FIG. 28 is a time chart of a temporal increase in scattering light;

FIG. 29 is a time chart obtained when a foreign substance adheres to theouter surface of the sensor body near the smoke-sensing point P;

FIG. 30 is a schematic diagram of a configuration of a smoke-sensingunit according to a fourth embodiment;

FIG. 31 shows a solid-angle arrangement of the configuration of thesmoke-sensing unit according to the fourth embodiment;

FIG. 32A shows a solid-angle arrangement of light axes of a firstlight-emitting element, a second light-emitting element, and alight-receiving element;

FIG. 32B shows the solid-angle arrangement of point A of the firstlight-emitting element and point C of the light-receiving element;

FIG. 32C shows the solid-angle arrangement of point B of the secondlight-emitting element and point C of the light-receiving element;

FIG. 33 shows experimental results of the amount of light-receivedsignals for different types of smokes when the scattering angle andpolarization angle are changed in the smoke-sensing unit having theconfiguration of FIG. 30;

FIG. 34 is a table of amount of light-received signal for differenttypes of combusted materials and ratio thereof when the polarizationdirection and the scattering angle are set;

FIG. 35 is a flowchart of a fire judgment process according to a fifthembodiment;

FIG. 36 is a graph of relation between light-received level against timefor smoke of tobacco in the conventional light scattering type smokesensor and including a smoke chamber;

FIG. 37 is a graph of relation between light-received level against timefor smoke of fire in the conventional light scattering type smoke sensorand including the smoke chamber;

FIG. 38 is a graph of relation between light-received level against timefor smoke of tobacco in the light scattering type smoke sensor accordingto the fifth embodiment; and

FIG. 39 is a graph of relation between light-received level against timefor smoke of fire in the light scattering type smoke sensor according tothe fifth embodiment.

DESCRIPTION OF NOTATIONS

-   1, 40, 100 light scattering type smoke sensor-   2, 112 sensor body-   3, 113 terminal board-   4, 41, 114 chamber base-   4 a, 108 smoke-sensing unit-   5, 109, 110, 125, 129 light-emitting element (first light-emitting    element, second light-emitting element)-   5 b, 42, 109 b light-emitting opening-   6, 111, 133 light-receiving element-   6 b, 43, 111 b light-receiving opening-   7 outer surface of sensor body-   9, 116 transparent cover-   11, 136 sensor base-   15, 102 notifying circuit-   16, 103 signal processing unit-   17, 104 storing unit-   18, 105, 106 light emission controlling unit (first light emission    controlling unit, second light emission controlling unit)-   19, 107 amplifying circuit-   20, 25, 30 comparator-   21, 24, 31 standard voltage source-   23 differentiating circuit-   26 monostable multivibrator-   27, 28, 29 AND gate-   126, 130 polarization filter

BEST MODE(S) FOR CARRYING OUT THE INVENTION

First, a light scattering type smoke sensor according to a firstembodiment will be described. FIG. 1 is a sectional view of the lightscattering type smoke sensor according to the first embodiment. In FIG.1, a smoke sensor 1 using scattering light schematically includes asensor body 2, a terminal board 3, a chamber base 4, a light-emittingelement 5, a light-receiving element 6, and a transparent cover 9.

The terminal board 3 is housed inside the sensor body 2, and a circuitboard 8 is housed inside the terminal board 3. The chamber base 4 isattached below the circuit board 8, and the chamber base 4 accommodatesthe light-emitting element 5 which serves as light-emitter, and thelight-receiving element 6 which serves as light-receiver.

An outer surface 7 of the sensor body is a lower surface of the chamberbase 4 and formed substantially flat, and the transparent cover 9 isattached to the outer surface 7 of the sensor body. Further, the outersurface 7 of the sensor body has a light-emitting opening 5 b forejecting the light emitted from the light-emitting element 5 to theoutside of the smoke sensor 1 using scattering light, and alight-receiving opening 6 b for introducing light thus ejected andscattered by smoke into the light-receiving element 6. In an outsideopen space further below the outer surface 7 of the sensor body, a lightaxis crossing point P is set, at which a light axis of thelight-emitting element 5 and a light axis of the light-receiving element6 mutually intersect with each other, and the light axis crossing pointP constitutes a smoke-sensing point. Thus, one of characteristics of thesmoke sensor 1 using scattering light according to the first embodimentis that the smoke-sensing point is set outside the smoke sensor 1 usingthe scattering light. Since the smoke-sensing space does not need to beformed inside the smoke sensor 1 using scattering light, a smoke chamberis not provided.

FIG. 2A shows a sensor base 11 which is a base for the attachment of thesmoke sensor 1 using scattering light. In FIG. 2A, the sensor base 11 isinstalled onto a ceiling surface 10 and the smoke sensor 1 usingscattering light of FIG. 1 is attached to the sensor base 11. As shownin FIG. 2A, since the smoke sensor 1 using scattering light does notinclude a smoke chamber which is embedded in the conventional lightscattering type smoke sensor, the entire smoke sensor 1 using scatteringlight is thinner by the amount of the smoke chamber, and the smokesensor 1 using scattering light does not protrude downward by asignificant amount when the smoke sensor 1 is installed onto the ceilingsurface 10 (in other words, the smoke sensor 1 using scattering lightcan be made relatively indistinctive against the ceiling surface 10).

FIG. 2B shows the sensor base 11 installed inside the ceiling surface 10and the smoke sensor 1 using scattering light of FIG. 1 embedded andattached to the sensor base 11. As shown in FIG. 2B, a lower surface(the outer surface 7 of the sensor body and the transparent cover 9 ofFIG. 1) of the smoke sensor 1 using scattering light can be arrangedsubstantially coplanar with the ceiling surface 10. In this case, thereis no protruding portion as the portion of the smoke chamber in theconventional smoke sensor. Hence a full-flat ceiling configuration canbe realized. Particularly, since the smoke chamber is not necessary andthe smoke sensor 1 using scattering light as a whole is made thinner, aportion embedded into the ceiling is smaller than in the conventionalsensor, whereby the smoke sensor 1 using scattering light can beinstalled onto a narrow ceiling space.

FIG. 3 is a perspective view of the chamber base 4 in which thelight-emitting element 5 and the light-receiving element 6 of FIG. 1 arearranged. In FIG. 3, the light-emitting opening 5 b and thelight-receiving opening 6 b are formed on the outer surface 7 of thesensor body on a side of smoke sensing of the chamber base 4, and thelight-emitting element 5 is embedded inside the light-emitting opening 5b, whereas the light-receiving element 6 is embedded inside thelight-receiving opening 6 b (light-emitting element 5 andlight-receiving element 6 are not shown in FIG. 3).

FIG. 4 is a sectional view of an entire smoke-sensing unit including thechamber base 4 of FIG. 3 (here, the transparent cover 9 is shown by animaginary line). In FIG. 4, an upper side of the chamber base 4 isformed as a flat outer surface 7 of the sensor body. In the outersurface 7 of the sensor body, the light emitting-opening 5 b and thelight-receiving opening 6 b open and the transparent cover 9 is attachedfor protection. In the first embodiment, the outer surface 7 of thesensor body is made flat at the side of the smoke-sensing point P in theoutside open smoke-sensing space, by way of example. The outer surface 7of the sensor body, however, may be made slightly curved or may havesome unevenness if necessary.

The light-emitting element 5 and the light-receiving element 6 areembedded inside the chamber base 4. A light axis 5 a of light emissionof the light-emitting element 5 intersects with a light axis 6 a oflight reception of the light-receiving element 6 at the smoke-sensingpoint P in the open smoke-sensing space outside the outer surface 7 ofthe sensor body. Here, height h from the outer surface 7 of the sensorbody to the smoke-sensing point P which is the crossing point of lightaxes in the outside space can be set to any value, and preferably set tosuch a height that a factor of disturbance does not affect the smokesensing. The factor of disturbance which may become obstacle for thesmoke sensing outside the smoke sensor 1 using scattering light is, forexample, dust or insect adhering to the outer surface 7 of the sensorbody. For example, the height h can be set to a maximum height of aninsect that gathers relatively frequently when the smoke sensor 1 usingscattering light is installed. For example, it is preferable to secureat least 5 mm as height h.

The chamber base 4 may be configured of an insect-avoiding material towhich insects rarely gather, or the insect-avoiding agent may be made topermeate or may be applied to the outer surface 7 of the sensor body.Here, the transparent cover 9 may be similarly configured by theinsect-avoiding material, or the insect-avoiding agent may be made topermeate or may be applied to the transparent cover 9. Thus, the insectscan be prevented from wriggling around on the outer surface of thetransparent cover 9, whereby the false alarm can be prevented from beingcaused by the presence of insects. Any ingredients can be used as aningredient of an actually applied insect-avoiding agent, and diethyltoluamide or pyrethroid may be applicable.

FIG. 5 is a circuit block diagram of the smoke sensor 1 using scatteringlight according to the first embodiment. In FIG. 5, the smoke sensor 1using scattering light includes a smoke-sensing unit 4 a having thelight-emitting element 5 and the light-receiving element 6 as describedabove, a notifying circuit 15, a signal processing unit 16 employing acentral processing unit (CPU), a storing unit 17, a light emissioncontrolling unit 18, and an amplifying circuit 19.

In the above-described configuration, in brief, the light-emittingelement 4 a is driven by the light emission controlling unit 18 to emitlight. Thus emitted light is reflected by smoke at the smoke-sensingpoint P outside the smoke sensor 1 using scattering light andsurroundings thereof, and scattered. The scattered light is received bythe light-receiving element 6. The output of the light-receiving element6 is amplified by the amplifying circuit (logarithmic amplifier) 19, andsupplied as an input to the signal processing unit 16. The signalprocessing unit 16 compares the output level of the light-receivingelement 6 supplied as an output from the amplifying circuit 19 with afire threshold TH1, a false alarm threshold TH2, or an obstaclethreshold TH3; the fire threshold TH1, the false alarm threshold TH2,and the obstacle threshold TH3 are stored in the storing unit 17 inadvance, as described later, to decide whether the fire occurs or not,whether it is a false alarm or not, or whether there is an obstacle ornot. When a predetermined condition is satisfied, the signal processingunit 16 operates the notifying circuit 15 to send out a fire signal to apredetermined receiver.

The signal processing unit 16 has a function of a fire judging unit 16 aas a function under programmed control. The fire judging unit 16 aperforms fire judgment, in other words, the fire judging unit 16 adecides whether the fire occurs or not based on the light-receivedsignal from the light-receiving element 6 and a differential valuethereof. Specifically, the fire judging unit 16 a decides that the fireoccurs when the light-received signal A from the light-receiving element6 exceeds the predetermined fire threshold TH1, and a differential valueB of the light-received signal A does not exceed the predetermined falsealarm threshold TH2.

On the other hand, when light-received signal A of the light-receivingelement 6 exceeds the predetermined fire threshold TH1, and thedifferential value of the light-received signal B exceeds thepredetermined false alarm threshold TH2, the fire judging unit 16 adecides whether the light-received signal A exceeds the predeterminedobstacle threshold TH3 or not when a predetermined time period T elapsessince the differential value B exceeds the predetermined false alarmthreshold TH2. When the light-received signal A is lower than theobstacle threshold TH3, the fire judging unit 16 a decides that theobstacle is temporal and continues monitoring. On the other hand, whenthe light-received signal A exceeds the obstacle threshold TH3, the firejudging unit 16 a decides that the obstacle is caused by foreignsubstance.

FIG. 6 is a time chart of light emission driving by the light emissioncontrolling unit 18 of FIG. 5. In FIG. 6, light-emission pulse (A)indicates the light emitted from the light-emitting element 5 of FIG. 1,the light-received signal (B) indicates the light received by thelight-receiving element 6 of FIG. 1, and synchronous light-receivedsignal (C) indicates an amplified version of a light-received signalacquired by amplification in the amplifying circuit 19 of FIG. 5.

Here, the light emission controlling unit 18 drives the light-emittingelement 5 so that the light-emitting element 5 emits light aslight-emission pulse (A) having pulse width T2 and being cyclicallyoutput every cycle T1. The light emission controlling unit 18 thus makesthe light-emitting element 5 perform modulated light emission.Accordingly, the amplifying circuit 19 synchronizes with the modulationof the light emission controlling unit 18, and acquires the synchronouslight-received signal (C) which is the light-received signal (B) insynchronization with the light emission modulation.

Here, the cycle T1 of light emission is, for example, T1=1 second, andthe pulse width T2 of the modulated light emission is, for example,T2=50 microseconds. Thus, the modulated light emission and thecorresponding synchronous light reception allow for elimination oflight-received signal generated by incidence of light other than thelight scattered by the smoke in the outside smoke-sensing space, andonly the scattered light by the smoke is surely received.

Further, since the light emission wavelength band of the light-emittingelement 5 is within the visible light band, the light emission timeperiod is restricted to a time period equal to or less than 1millisecond so that the human cannot recognize the intermittentlyemitted light. For the human to visually recognize the light from thelight-emitting element, the light must be emitted continuously over morethan 1 millisecond. Here, the light emission time period is restrictedto a time period equal to or less than 1 millisecond, so that the humancannot see the light from the light-emitting element.

In the case of light-emission pulse (A) of FIG. 6, it is sufficient toset the total light emission time period of three light-emission pulses(pulse width T2×3) to a time period equal to or less than 1 millisecond.For example, if T2=50 microseconds as described above, the total lightemission time period of three light-emission pulses is 150 microseconds,which is less than 1 millisecond. Hence the emitted light cannot beseen.

FIG. 7 is a circuit block diagram in which the processing function ofthe fire judging unit 16 a in the signal processing unit 16 of FIG. 5 isrealized by hardware. In FIG. 7, the fire judging unit 16 a configuredby hardware includes a comparator 20, a standard voltage source 21, adifferentiating circuit 23, a comparator 25, a standard voltage source24, a comparator 30, a standard voltage source 31, a monostablemultivibrator 26, AND gates 27, 28, 29, and the like connected with eachother as shown.

The comparator 20 receives as an input the amplified light-receivedsignal A which is obtained through amplification of the light-receivedoutput from the light-emitting element 6 at the amplifying circuit 19,compares the amplified light-received signal A with the predeterminedfire threshold TH1 set by the standard voltage source 21, and outputs asignal of H level (High output) when the level of the amplified receivedsignal A exceeds the fire threshold TH1. The H level output of thecomparator 20 is supplied to one input of the AND gate 27.

The comparator 30 receives as an input the amplified light-receivedsignal A which is obtained by amplification of the received light outputof the light-receiving element 6 at the amplifying circuit 19, comparesthe amplified light-received signal A with the obstacle threshold TH3set by the standard voltage source 31, and outputs a signal of H levelwhen the level of the amplified light-received signal A exceeds theobstacle threshold TH3. The H level output of the comparator is suppliedto one input of the AND gate 28.

The light-received signal A is differentiated by the differentiatingcircuit 23. The differentiated signal is supplied to the comparator 25via diode D1 as the differential value B. The comparator 25 compares thepredetermined abnormal threshold TH2 set by the standard voltage source24 and the differential value B. When the differential value B exceedsthe abnormal threshold TH2, the comparator 25 supplies a signal of Hlevel as an output. Here, the diode D1 obtains differentiated signalwith both positive polarity and negative polarity from thedifferentiating circuit 23, and takes out only the differential value ofpositive polarity.

The H level output from the comparator 25 is supplied to the monostablemultivibrator 26. The monostable multivibrator 26 is driven whenreceiving the H level output, and supplies H level output from output Qover a predetermined time period T. The signal supplied from the outputQ of the monostable multivibrator 26 is inverted and supplied to anotherinput of the AND gate 27.

Hence, when the differential value B exceeds the abnormal threshold TH2at the comparator 25, and the monostable multivibrator 26 supplies Hlevel output for time period T1, the AND gate 27 prohibits an output ofa fire-sensing signal of H level supplied from the comparator 20.Further, when the differential value B does not exceed the abnormalthreshold TH2 at the comparator 25, the signal from the output Q of themonostable multivibrator 26 is at L level (Low level). Hence, the ANDgate 27 is in a permission state so as to output the H level outputsupplied from the comparator 20 as it is to indicate fire sensing.

The output of the AND gate 27 is supplied to one input of the AND gate29. The output of the AND gate 28 is inverted and supplied to anotherinput of the AND gate 29. The AND gate 28 receives the output from thecomparator 30 and the inverted output from the monostable multivibrator26. Hence, the AND gate 28 turns into the permission state in responseto the inverted output provided when the monostable multivibrator 26,after operating for T time period according to the H level output fromthe comparator 25, is turned off, while the comparator 30 successivelysupplies the H level output by detecting the obstacle. Then, the outputof the comparator 30 is supplied as an output from the AND gate 28,which serves as an obstacle signal.

Further, when the AND gate 28 supplies the obstacle signal which is theH level output, the AND gate 29 is in a prohibited state due to theinverted input thereof. The H level output from the comparator 30 isprohibited by the AND gate 29, and when the obstacle signal is output,the output of the fire signal is prohibited.

FIG. 8 is a time chart of an operation of the fire judging unit 16 a ofFIG. 7 when the smoke sensor receives smoke of fire.

When the smoke sensor received the smoke of fire, the light-receivedsignal A of the light-receiving element 6 gradually increases over thetime as shown in section (A) of FIG. 8. When the light-received signal Aexceeds the fire threshold TH1 at time t1, the output of the comparator20 attains H level. Then, since the AND gates 27 and 29 are inpermission state, the fire signal attains H level as shown in section(C) of FIG. 8, and the notifying circuit 15 of FIG. 5 operates to sendout the fire signal to the receiver side.

Here, the differential value B of the light-received signal A of thedifferentiating circuit 23 is relatively small and does not exceed theabnormal threshold TH2 since the increase in smoke concentration isrelatively mild.

FIG. 9 is a time chart obtained when the scattered light temporarilyincreases due to flying insect passes over the smoke-sensing point P inthe outside open space below the outer surface 7 of the sensor body inthe smoke sensor 1 using scattering light of FIG. 1. When the scatteredlight is temporarily generated, the light-received signal A suddenlyincreases and then returns to a normal level as shown in section (A) ofFIG. 9. While the light-received signal A is above the fire thresholdTH1, the output of the comparator 20 attains H level as shown in section(C) of FIG. 9.

On the other hand, the differential value B of the light-received signalA at the differentiating circuit 23 rises by a significant degree to apositive direction at the rising of the light-received signal A, and islowered significantly to a negative direction at the falling of thelight-received signal B as shown in section (B) of FIG. 9. When thedifferential value B significantly changes to the positive direction,the level thereof exceeds the abnormal threshold TH2, and the comparator25 supplies an H level output as shown in section (D) of FIG. 9. As aresult, the output from the output Q of the monostable multivibratorattains H level as shown in section (E) of FIG. 9.

Hence, even when the output of the comparator 20 attains H level, asignal from the output Q of the monostable multivibrator 26 attains Hlevel, thereby prohibiting the output of the fire signal from the ANDgate 27. As a result, even when the insect or the like temporarilypasses over the smoke-sensing point P in the outside open space, thefalse alarm, i.e., the output of the fire signal does not happen.

The set time T of the monostable multivibrator 26 may be set so that thetime required for the foreign substance to pass through thesmoke-sensing point is sufficiently covered. The foreign substancepasses over the smoke-sensing point outside, for example, when theperson's finger or a matter other than the insect passes over thesmoke-sensing point.

FIG. 10 is a time chart obtained when the foreign substance such as acurtain adheres to the outer surface 7 of the sensor body near thesmoke-sensing point P set in the outside space of FIG. 1. When theforeign substance fixedly adheres, the light-received signal rises by asignificant degree over the fire threshold TH1 as shown in section (A)of FIG. 10 and exceeds and maintains a level over the obstacle thresholdTH3.

The differential value B output from the differentiating circuit 23changes by a significant degree to a positive direction as shown insection (B) of FIG. 10, and temporarily exceeds the abnormal thresholdTH2. Hence, the comparator 25 for the abnormal sensing also supplies Hlevel output according to the temporal increase in the differentialvalue, to operate the monostable multivibrator 26, and then themonostable multivibrator 26 supplies H level output for a predeterminedtime period T as shown in section (E) of FIG. 10.

Then due to the signal supplied from the output Q of the monostablemultivibrator 26, the AND gate 27 attains prohibited state, and does notsupply H level output while the monostable multivibrator 26 operates.When the monostable multivibrator 26 is turned off after a predeterminedtime period to supply L level output from the output Q, the prohibitionof the AND gate is canceled, and H level output is supplied. At the sametime, the AND gate 28 attains permission state at the rising of theinverted output of the monostable multivibrator 26 to the H level. Then,the AND gate 28 supplies the H level output on receiving the H leveloutput from the comparator 30 since the level of the light-receivedsignal A is over the obstacle threshold TH3. Then, the H level output ofthe AND gate 28 is supplied as the obstacle signal (trouble signal) asan output.

Simultaneously, the H level output of the AND gate 28 turns the AND gate29 into prohibited state, and even when the H level output is providedfrom the AND gate 27, the output thereof is prohibited and not suppliedas the fire signal.

The obstacle signal generated by the H level output of the AND gate 28is supplied to the notifying circuit 15 of FIG. 5. When the obstaclesignal is sent in a different signal form from the signal sent as thefire alarm to the receiver, the receiver side can give anobstacle-indicating display to notify the trouble of the sensor. Then,personnel can check the outer surface 7 of the sensor body on the sideof smoke sensing and remove the adhered foreign substance or the like toeliminate the trouble. The notifying circuit 15 may realize thetransmission of the obstacle signal to the receiver by making anotifying electric current flow as pulses for a predetermined timeperiod, for example.

Here, the output control of the fire signal or the obstacle signal maybe realized by software logic other than the wired logic shown in FIG.7. FIG. 11 shows a flowchart of programmed controlled processing of thefire judging unit 16 a in the signal processing unit 16 of FIG. 5. By aprogram different from that executes the fire judgment process of FIG.11, sampling of the light-received signal A supplied from the amplifyingcircuit 19 and the computation of the differential value through thedifferentiating process of the sampled light-received signal value arerepeatedly performed.

In the fire judgment process of FIG. 11, it is checked whether thereceived light value A is below the predetermined fire threshold TH1 ornot in step SA1. When the received light value A exceeds the firethreshold TH1, the process proceeds to step SA2, to check whether thedifferential value B is below the predetermined abnormal threshold TH2or not. When the differential value B is below the abnormal thresholdTH2, the process proceeds to step SA3, and it is decided that the fireoccurs and the output is supplied to indicate that there is a fire.

When the differential value B exceeds the abnormal threshold TH2 in stepSA2, the process proceeds to step SA4, and the timer set to the set timeT starts counting. After the timer starts, the elapse of the set time Tis checked in step SA5. When the set time elapses, the process proceedsto step SA6 to check whether the received light value A exceeds theobstacle threshold TH3 or not.

When the received light value A is not above the obstacle threshold TH3,similarly to the case shown in FIG. 9, it means that the increase inreceived light is caused merely by a temporal increase of scatteredlight, and no particular output is supplied regarding fire occurrence.On the other hand, when the received light value A exceeds the obstaclethreshold TH3, the abnormal light-received signal is successivelyobtained as shown in FIG. 10. Then, it is determined that the obstacleexists in step SA7, and the output is supplied to indicate the presenceof the obstacle.

In the first embodiment, as shown in FIG. 5, the received light outputfrom the light-receiving element 6 is amplified by the amplifyingcircuit 19 which is a logarithmic amplifier, whereby it can be decidedwhether the fire occurs or not even more accurately. When the receivedlight output is amplified by a normal linear amplifier, the amplifieroutput may become saturated under the environment with a strongdisturbing light, and false fire alarms may be raised. In the firstembodiment, since the received light output is amplified by alogarithmic amplifier, even when a relatively strong disturbing lightcomes into the light-receiving unit, the amplifier output would notbecome saturated and the sensor does not become incapable of detectingthe scattered light by the smoke. In addition, when the scattered lightby the smoke is detected by the logarithmic amplifier under theenvironment with disturbing light, the range of variation in theamplifier output corresponding to the smoke becomes small. Since thesmoke sensor of the first embodiment calculates the differential value,signal to noise (S/N) ratio is improved and it can be decided whetherthe fire occurs or not.

Thus, according to the first embodiment, since the smoke chamber iseliminated, the light scattering type smoke sensor can be configuredinto a flat shape with little protrusions, and a full-flat installation,i.e., an installation without protrusions from the ceiling surface canbe realized.

Further, since it is decided whether the fire occurs or not based on thereceived light amount and the differential value thereof, even when theforeign substances such as insects are present in the smoke-sensingspace, false alarm of the smoke sensor can be prevented, and the problemcaused by the use of an open space as the smoke-sensing space can beeliminated.

Further, since the sensor does not decide immediately that fire occurseven when the received light amount reaches the fire level, and decidesthat fire occurs based on a condition that the differential value of thereceived light amount is not higher than the abnormal threshold, falsealarm which may be caused by the presence of foreign substances such asinsects in the smoke-sensing space can be even more surely prevented.

Further, when the differential value remains at the level above theabnormal threshold even after the elapse of a predetermined time period,the sensor decides that there is an obstacle and gives a notification,whereby the maintenance and check of the smoke sensor can be realized.

Further, since the smoke-sensing point is set away from the sensor bodyby at least 5 mm, even when the dust adheres to the outer surface of thesensor body or the insect wriggles on the outer surface of the sensorbody, such foreign substances do not affect the fire sensing.

Further, since at least a portion of the outer surface of the sensorbody is configured by the insect-avoiding material or the like, theinsects rarely approaches the outer surface and the false alarm can beprevented in advance.

Further, since the angle of field of view of the light-receiver is setwithin 5 degrees, the size of the area for the scattered light sensingin the smoke-sensing space can be set to a requisite minimum so that theinfluence of the outside light can be prevented.

Further, since the light-received signal is amplified by the logarithmicamplifier, the amplified output of the light-received signal would notbe saturated, and the stable fire sensing can be realized.

Further, since the light-emitting element is intermittently driven toemit light by the modulated light emission signal, and thelight-received signal is amplified in synchronization with the modulatedlight emission signal, the illumination light or the like that wouldcause false alarm can be eliminated from the target of sensing, wherebythe false alarm can be surely prevented from being caused by the outsidelight.

Further, since the light-emission pulse width is set within the range of1 millisecond, the light emission time period can be suppressed to sucha time period that the light is imperceptible for the visiblesensitivity of human, whereby the blinking of the light-emitting unit ofthe smoke sensor can be made unrecognizable for human.

Further, since the total light emission time period at the intermittentlight emission driving is set within the range of 1 millisecond, thelight emission time period can be suppressed to an imperceptible rangefor the visible sensitivity of human, whereby the blinking of thelight-emitting unit of the smoke sensor can be made unrecognizable forhuman.

Next, a light scattering type smoke sensor according to a secondembodiment will be described. The second embodiment is basically similarto the first embodiment. The second embodiment, however, is differentfrom the first embodiment in that the light axis of the light-emittingelement and the light axis of the light-receiving element are arrangedso as to intersect at a predetermined angle on the outer surface of thesensor body, since the first embodiment arranges the light axis of thelight-emitting element and the light axis of the light-receiving elementsubstantially linearly on the outer surface of the sensor body. Theconfiguration and the method of the second embodiment are similar tothose of the first embodiment if not specifically described otherwise,and the components with the similar function will be referred to by thesame names or denoted by the same reference characters as the firstembodiment.

FIG. 12 is a perspective view of a chamber base 41 of a smoke sensor 40using scattering light (partly shown) according to the secondembodiment. On the chamber base 41, a light-emitting opening 42 and alight-receiving opening 43 are arranged so as to intersect with eachother at a predetermined angle on the outer surface of the sensor body.The light-emitting element 5 not shown is housed inside thelight-emitting opening 42, whereas the light-receiving element 6 notshown is housed inside the light-receiving opening 43.

Next, a relation between light emitting angle and light receiving anglewill be described in detail. It should be noted that the presentapplication incorporates Japanese Patent Application (JP-A) No.2002-4221 filed on Jan. 11, 2002 by the present applicant, and a part ofthe description below is disclosed in the JP-A 2002-4221.

FIG. 13A schematically shows an optical positional relationcorresponding to the positions at which the light-emitting unit and thelight-receiving unit are installed in the chamber base 41 of FIG. 12 asa representation in the three-dimensional coordinate space.

In FIG. 13A, a light axis 13 of light emission from light-emitting pointO of the light-emitting element 5 is shown by a vector, and a light axis14 of light reception along which the scattered light comes from thelight axis crossing point P located in the outside open space is shownby a vector towards light-received point Q of the light-receivingelement 6. Further, among the angles formed by the intersecting lightaxis 13 of light emission and the light axis 14 of light reception, anangle formed by light coming along the light axis 13 of light emissionis scattered by smoke or the like and changes the direction so as toproceed along the light axis 14 of light reception is represented as ascattering angle θ, and a supplementary angle of the scattering angle θis represented as a configuration angle δ(θ=180 degrees−δ).

In FIG. 13A, a triangle drawn by connecting the light-emitting point O,the light axis crossing point P, and the light-receiving point Q formsan imaginary optical plane for the smoke sensing using scattering lightaccording to the second embodiment. The plane forming the triangle OPQis arranged so as to form a certain angle with each of xy plane(horizontal plane) and zx plane (vertical plane).

Here, for the simplicity of description, the plane is arranged so thatthe projection of the light-emitting point O over the x-axis isprojection point A, and an inclined angle φ formed by the light axis 13of light emission and the vertical direction is an angle formed by thelight axis 13 and the x-axis.

When the light axis 13 of light emission and the light axis 14 of lightreception are viewed from the horizontal plane which is the xy plane,the projection point A corresponds to the light-emitting point O and aprojection point B corresponds to the light-receiving point Q as shownin FIG. 13B. In other words, the light axis 13 of light emission and thelight axis 14 of light reception intersect with each other at apredetermined angle α (apparent configuration angle α on the horizontalplane) in a horizontal direction.

When the coordinate of the light-emitting point O is set as (a₁, b₁, c₁)and the coordinate of the light-receiving point Q is set as (a₂, b₂,c₂), the configuration angle δ, the apparent configuration angle α onthe horizontal plane, and the inclination angle φ in the verticaldirection can be represented by following expressions (1) to (3):$\begin{matrix}\left\lbrack {{Expression}\quad 1} \right\rbrack & \quad \\{{\cos\quad\delta} = \frac{{a_{1}a_{2}} + {b_{1}b_{2}} + {c_{1}c_{2}}}{\sqrt{a_{1}^{2} + b_{1}^{2} + c_{1}^{2}}\sqrt{a_{2}^{2} + b_{2}^{2} + c_{2}^{2}}}} & {{ex}\quad(1)} \\\left\lbrack {{Expression}\quad 2} \right\rbrack & \quad \\{{\cos\quad\alpha} = \frac{{a_{1}b_{1}} + {a_{2}b_{2}}}{\sqrt{a_{1}^{2} + b_{1}^{2}}\sqrt{a_{2}^{2} + b_{2}^{2}}}} & {{ex}\quad(2)} \\\left\lbrack {{Expression}\quad 3} \right\rbrack & \quad \\{{\tan\quad\phi} = \frac{c_{1}}{a_{1}}} & {{ex}\quad(3)}\end{matrix}$

For example, when the inclination angle φ in the vertical direction isset to 30°, and the apparent configuration angle α on the horizontalplane is set to 120°, the configuration angle δ becomes 97°. When theapparent configuration angle α on the horizontal plane is set to 120°,and the inclination angle φ is set to 9.8°, the configuration angle δbecomes 117°.

In brief, when the apparent configuration angle α is maintained at aconstant value 120°, the inclination angle φ is 9.8°, 30°, and theactual configuration angle δ is 117°, 97°. When the positions of thelight-emitting point O and the light-receiving point Q in the horizontaldirection are not changed, and the inclination angle φ in verticaldirection is made larger, the actual configuration angle δ is madesmaller on the contrary. Needless to say, when the inclination angle φin the vertical direction is made smaller, the height of the light axiscrossing point O becomes lower, and the sensor becomes thinner.

Based on the three-dimensional relation of optical axes from the lightemission to the light reception as shown in FIGS. 13A and 13B, theconfiguration angle δ of the light axis 13 of light emission and thelight axis 14 of light reception is made approximately 110° in thesecond embodiment. When the configuration angle δ=110°, thecorresponding scattering angle θ is 70°, i.e., 18°−δ. The configurationangle δ is set to 110° (θ=70°) for the following reasons. Thesmoke-sensing unit of the light scattering type smoke sensor is requiredto satisfy two contradictory needs: (1) to increase the amount ofscattered light by smoke, and (2) to suppress the influence by thedifference in the types of the smoke. The inventor found the relationbetween the scattering angle and the amount of scattered light forvarious types of smoke based on experiments and simulations(OPTIMIZATION OF SENSITIVITY CHARACTERISTICS OF PHOTOELECTRIC SMOKEDETECTOR TO VARIOUS SMOKES, Nagashima et al., Asia Oceania FireSymposium, 1998).

FIG. 14 shows the variation in the amount of scattered light accordingto the scattering angle θ (=180°−δ), and shows the relation between thescattering angle and the amount of scattered light for various types ofsmokes by a relative ratio, wherein the amount of scattered light by thefumigation smoke of the filter paper at the scattering angle=40° in theconventional light scattering type smoke sensor is set as one. As shownin FIG. 14, along with the increase in the scattering angle, the amountof scattered light decreases. For the stabilization of the operation ofthe smoke sensor, at least ⅕ the amount of scattered light in theconventional sensor needs to be secured, and θ<90° needs to hold. On theother hand, for the suppression of influence by the types of smokes, theoutput of the kerosene combustion smoke needs to be larger compared withthe output of the filter paper fumigation smoke shown in FIG. 15 as muchas possible. The sensitivity for the kerosene combustion smoke isrequired to be at least 1/7 the sensitivity for the filter paper, and inthis case θ>50°. This is an ideal condition to pass various fire testregulated by EN standard and UL standard. The scattering angle thatsatisfies both standards is 50°<θ<90°, and ideally, θ=70°.

Thus the second embodiment attains the same effect as the firstembodiment. Moreover, according to the second embodiment, when the lightaxis 13 of light emission of the light-emitting element 5 and the lightaxis 14 of light reception of the light-receiving element 6 are arrangedat the configuration angle δ=110°, and embedded into the chamber base 41so that the apparent configuration angle α in the horizontal surface andthe inclination angle φ in the vertical direction are set, even if theangular arrangement is made optimal so that there is little influence ofthe size of the smoke particle on the sensitivity, the amount ofprotrusion of the light axis crossing point P with respect to the smokecan be suppressed.

Next, a light scattering type smoke sensor according to a thirdembodiment will be described. The light scattering type smoke sensoraccording to the third embodiment is different from the light scatteringtype smoke sensor according to the first or the second embodiment whichincludes only one light-emitting element, since the smoke sensoraccording to the third embodiment schematically includes twolight-emitting elements. The configuration and the method of the thirdembodiment are similar to those of the second embodiment if notspecified otherwise, and the components with the similar functions arereferred to by the same names or denoted by the same referencecharacters as the second embodiment.

First, the reason for providing two light-emitting elements isdescribed. The conventional light scattering type smoke sensor sometimesraises false fire alarm when sensing the smoke of cooking, the steam ofthe bathroom, or the like, other than the smoke of fire.

It is known to direct two different types of light with differentwavelengths onto the smoke-sensing space, thereby finding the ratio oflight intensities of two different types of scattered light withdifferent wavelengths to distinguish the types of the smoke, or todirect light with a vertical polarization plane and light with aparallel polarization plane with respect to the scattering plane,thereby finding the ratio of light intensities of respectivepolarization components of the light scattered by the smoke todistinguish the types of the smoke in order to prevent such false firealarm from being caused by other factors than the fire.

In the conventional method of distinguishing the types of smoke usingthe light with different wavelengths or the light with the differentpolarization planes, however, the accuracy of distinction between thesmoke of fire and the smoke of non-fire, such as steam of cooking andthe steam of a bathroom is not sufficient. Hence, a more highly accuratesmoke distinction is desirable.

Hence, in the third embodiment, in addition to the elimination of thesmoke chamber in the smoke sensor for realization of a thinner andsmaller smoke sensor, one of the objects is improvement in accuracy ofsmoke distinction for realization of secure prevention of non-firealarm.

Next, the light scattering type smoke sensor according to the thirdembodiment will be described. FIG. 16 is a sectional view of the lightscattering type smoke sensor according to the third embodiment. Thesmoke sensor 100 using scattering light schematically includes a sensorbody 112, a terminal board 113, a chamber base 114, a firstlight-emitting element 109, a second light-emitting element 110 (notshown in FIG. 16), a light-receiving element 111, and a transparentcover 116. If not specified otherwise, the sensor body 112, the terminalboard 113, the chamber base 114, the first light-emitting element 109,the light-receiving element 111, and the transparent cover 116 can beconfigured similarly to the sensor body 2, the terminal board 3, thechamber base 4, the light-emitting element 5, the light-receivingelement 6, and the transparent cover 9, and the second light-emittingelement 110 can be configured similarly to the light-emitting element 5.

Here, the first light-emitting element 109 and the second light-emittingelement 110 as plural light emitters, and the light-receiving element111 as the light receivers are housed in the chamber base 114. Further,two light-emitting openings 109 b, 110 b (only one light emittingopening 109 b is shown in FIG. 16) for ejecting the light emitted fromthe first light-emitting element 109 and the second light-emittingelement 110 to the outside of the smoke sensor 100 using scatteringlight, and a light receiving opening 111 b for introducing the lightthus ejected and scattered by the smoke into the light-receiving element111 are formed in an outer surface 118 of the sensor body. In theoutside open space further below the outer surface 118 of the sensorbody, light axis crossing point P where the light axes of the firstlight-emitting element 109 and the second light-emitting element 110intersect with the light axis of the light-receiving element 111 is set,and the light axis crossing point P forms the smoke-sensing point.

When the sensor base (not shown) which is the base for the attachment ofthe smoke sensor 100 using scattering light is installed on the ceilingsurface (not shown) and the smoke sensor 100 using scattering lightshown in FIG. 16 is attached to the sensor base, there is no protrudingportion of the smoke chamber similarly to the first embodiment shown inFIG. 2A, whereby the smoke sensor 100 using scattering light can beinstalled to the ceiling surface in such a manner that the smoke sensor100 does not stand out.

Further, when the sensor base is installed inside the ceiling surfaceand the smoke sensor 100 using scattering light of FIG. 16 is embeddedand attached to the sensor base, similarly to the first embodiment ofFIG. 2B, the lower surface of the smoke sensor 100 using scatteringlight is coplanar with the ceiling surface and there is no protrudingportion, whereby the full-flat ceiling configuration can be realized.Particularly, the portion to be embedded in the ceiling surface becomessmaller than in the conventional sensor, whereby the smoke sensor 100using scattering light can be arranged to the narrow ceiling space.

FIG. 17 is a perspective view of the chamber base 114 which is employedfor the solid-angle arrangement of the first light-emitting element 109,the second light-emitting element 110, and the light-receiving element111. In FIG. 17, the first light-emitting opening 109 b, the secondlight-emitting opening 110 b, and the light-receiving opening 111 b areformed on the outer surface 118 of the chamber base 114, and the firstlight-emitting element 109, the second light-emitting element 110, andthe light-receiving element 111 are embedded inside respective openings(those elements are not shown in FIG. 17).

FIG. 18 is a sectional view of the entire smoke-sensing unit in thesolid-angle arrangement in which the chamber base 114 of FIG. 17 isemployed (sectional view along the section passing through the firstlight emitting-opening 109 b and the light-receiving opening 111 b. Thetransparent cover 116 is shown by an imaginary line). In FIG. 18, anupper portion of the chamber base 114 is formed as the flat outersurface 118 of the sensor body, and the first light-emitting opening 109b, the second light-emitting opening 110 b, and the light-receivingopening 111 b are formed therein, with the transparent cover 116attached for protection.

The first light-emitting element 109, the second light-emitting element110 (not shown in FIG. 18), and the light-receiving element 111 areembedded inside the chamber base 114, and the light axis 109 a of thefirst light-emitting element 109, the light axis 110 a of the secondlight-emitting element 110 (not shown in FIG. 18), and the light axis111 a of the light-receiving element 111 form a solid crossing with eachother at the smoke-sensing point P in the open smoke-sensing spaceoutside the outer surface 18 of the sensor body.

Here, the height h from the outer surface 118 of the sensor body to thesmoke-sensing point P which is the light axis crossing point in theoutside space may be set to such a height that the substance adhering tothe outer surface 7 of the sensor body does not affect the smoke sensingsimilarly to the first embodiment. Preferably, h is set to a heightequal to or longer than 5 mm, for example.

FIG. 19 is a circuit block diagram of the light scattering type smokesensor according to the third embodiment. In FIG. 19, the smoke sensor100 using scattering light includes a notifying circuit 102, a signalprocessing unit 103 using a micro processing unit (MPU), a storing unit104, a first light emission controlling unit 105, a second lightemission controlling unit 106, an amplifying circuit 107, and asmoke-sensing unit 108. If not specified otherwise, the notifyingcircuit 102, the signal processing unit 103, the storing unit 104, thefirst light emission controlling unit 105, the amplifying circuit 107,and the smoke-sensing unit 108 can be similarly configured as thenotifying circuit 15, the signal processing unit 16, the storing unit17, the light emission controlling unit 18, the amplifying circuit 19,and the smoke-sensing unit 4 a, and the second light emissioncontrolling unit 106 can be similarly configured as the light emissioncontrolling unit 18.

The smoke-sensing unit 108 includes the first light-emitting element109, the second light-emitting element 110, and the light-receivingelement 111. The first light-emitting element 109, the secondlight-emitting element 110, and the light-receiving element 111 arearranged so that the light axes thereof intersect with each other at thesmoke-sensing point P set in the open space outside the smoke sensor.

FIG. 20A shows the solid-angle arrangement of light axes 109 a and 110 afor light emission of the first light-emitting element 109 and thesecond light-emitting element 110, and a light axis 111 a for lightreception of the light-receiving element 111.

The smoke-sensing point P where the light axes 109 a and 110 a of lightemission and the light axis 111 a of light reception intersect with eachother exists in the open smoke-sensing space outside the outer surface118 of the sensor body of the chamber base 114 of FIG. 17, whereas thefirst light-emitting element 109, the second light-emitting element 110,and the light-receiving element 111 are arranged inside the chamber base114.

FIG. 20B shows the solid-angle arrangement of point A of the firstlight-emitting element 109 and point C of the light-receiving element111. Here, a plane including the light axis 109 a of light emission fromthe point A of the first light-emitting element 109 and the light axis111 a of light reception from the point C of the light-receiving element111 is represented by triangle PCA, and an angle formed by the lightaxis 109 a of light emission and the light axis 111 a of light receptionin the plane including the triangle PCA is a first scattering angle θ1of the first light-emitting element 109.

FIG. 20C shows the solid-angle arrangement of point B of the secondlight-emitting element and point C of the light-receiving element 111.Here, the light axis 110 a of light emission and the light axis 111 a oflight reception exist in the plane including the triangle PCB, and thescattering angle formed by the light axis 110 a of light emission andthe light axis 111 a of light reception is represented as a scatteringangle θ2 which is formed by the light axis 110 a of light emission andthe light axis 111 a of light reception in the plane including thetriangle PCB.

For the simplicity of description of the configuration of thesmoke-sensing unit 108 having the solid-angle arrangement of FIGS. 20Ato 20C, it is assumed that the light axes of the first light-emittingelement 109, the second light-emitting element 110, and thelight-receiving element 111 exist in the same plane as shown in FIG. 21.

In FIG. 21, the first light-emitting element 109 is set so as to havethe first scattering angle θ1 as θ=30°, wherein the first scatteringangle θ1 is formed by the light axis 109 a of light emission of thefirst light-emitting element 109 and the light axis 111 a of lightreception of the light-receiving element 111 with respect to thecrossing point P thereof in the third embodiment. Further, a nearinfrared light emitting diode (LED) is employed as the firstlight-emitting element 109, and the light emitted from the firstlight-emitting element 109 is set so that the central wavelength isλ1=900 nm (=0.9 μm) in the third embodiment.

In the third embodiment, in addition to the first light-emitting element109, the second light-emitting element 110 is provided. The secondlight-emitting element 110 is set so that the second scattering angle θ2formed by the light axis 110 a of light emission of the secondlight-emitting element 110 and the light axis 111 a of light receptionof the light-receiving element 111 with respect to the crossing point Pthereof is larger than the first scattering angle θ1 of the firstlight-emitting element 109 and the light-receiving element 111 (θ2>θ1).In the third embodiment, the second scattering angle θ2 is set to 120°.

A visible light LED is employed for the second light-emitting element110. When the central wavelength of the light emitted from the secondlight-emitting element 110 is referred to as second wavelength λ2, thewavelength λ2 is set shorter than the wavelength λ1 of the firstlight-emitting element 109. In the third embodiment, λ2=500 nm (=0.5μm).

Further, it is desirable that a laser diode which emits collimatedparallel beam be employed as the first light-emitting element 109 andthe second light-emitting element 110. Further, an element with anarrower angle of field of view with respect to the smoke-sensing pointP is preferably used as the light-receiving element 111. The angle offield of view is, for example, not more than 5 degrees. When the angleof field of view is set to such range, the light from only therestricted smoke-sensing space around the smoke-sensing point P isreceived, and the amount of disturbing light other than the scatteredlight of smoke incident on the light receiving unit can be reduced andthe influence by the outside light can be minimized. With thisconfiguration, the light scattering type smoke sensor can reduce therisk of false alarm by the disturbing light, such as the illuminationlight or the reflected light of sunlight. Further, since the amount ofreceived disturbing light can be suppressed, the risk of the amplifyingcircuit 107 of FIG. 19 reaching the saturated level can be reduced.

FIG. 22 shows a relation between the angle of field of view and the areaof field of view, wherein the horizontal axis represents the angle offield of view of the light scattering type smoke sensor when the lightscattering type smoke sensor is installed on the ceiling surface of theheight of approximately 3 m for monitoring, and the vertical axisrepresents the area (area of field of view) of the floor surfaceincluded in the field of view of the light scattering type smoke sensor.As shown in FIG. 22, when the angle of field of view is 5 degrees, thearea of field of view is approximately 2200 cm², whereas when the angleof field of view is 20 degrees, the area of field of view isapproximately 38000 cm². Then the amount of received disturbing lightincreases by the area ratio if the illumination light or the like in theroom is uniform, and along with the increase in the angle of field ofview, the risk of the amplifying circuit 107 of FIG. 19 reaching thesaturated level dramatically increases in a manner of quadric function.

Further, though it is preferable that the angle of field of view of thelight-receiving unit be narrow for the reduction of influence of thedisturbing light, when a lens-attached photodiode or a phototransistoris employed as the light-receiving element 111, it is prerequisite thatthe angle of field of view is not more than 5 degrees. On the otherhand, when the angle of field of view is narrower than is required, theamount of received light of the scattered light of smoke itself becomessmall, whereby the S/N ratio is degraded. Hence, the angle of field ofview of the light-receiving unit is preferably not more than 5 degrees.

FIG. 23 is a graph of scattering efficiency I of the light from thefirst light-emitting element 109 and the second light-emitting element110 by the fumigation smoke (white smoke) generated by the combustion ofcotton lampwick against the scattering angle θ, which is observed in thesmoke-sensing unit with the configuration as shown in FIGS. 16 to 21.The horizontal axis in FIG. 23 represents the scattering angle θ (whereθ=0° ˜180°), and the vertical axis represents the scattering efficiencyI in the logarithmic coordinate.

When the light emitted from the first light-emitting element 109 has thefirst wavelength λ1=900 nm, the scattering efficiency at the side of thelight-receiving element 111 appears as a characteristic curve 20. On theother hand, when the light emitted from the second light-emittingelement 110 has the second wavelength λ2=500 nm, the scatteringefficiency at the side of the light-receiving element 111 appears as acharacteristic curve 21.

When the characteristic curves 20 and 21 are examined with respect tothe wavelength of the light emitted from the light-emitting element, itcan be seen that the characteristic curve 13 of the wavelength λ1=900 nmof the first light-emitting element 109 has a lower scatteringefficiency, whereas the characteristic curve 14 of the shorter secondwavelength λ2=500 nm of the second light-emitting element 110 has ahigher scattering efficiency.

On the other hand, with respect to the variation in the scattering angleθ of the characteristic curves 20 and 21 of the scattering efficiency ofthe first and the second light-emitting elements 109 and 110, both showsa higher scattering efficiency for the smaller scattering angle θ, andthe scattering efficiency decreases along with the increase in thescattering angle. The scattering efficiency hit the lowest value whenthe scattering angle is approximately 120°. Then, along with theincrease in the scattering angle, the scattering efficiency increases.

In the third embodiment, the scattering angle θ1 of the firstlight-emitting element 109 is set to 300, whereby the scatteringefficiency A1 is obtained at the point P1 in the characteristic curve20. On the other hand, with respect to the second light-emitting element110, the second scattering angle θ2 is set to 120°, whereby thescattering efficiency A2 is obtained at the point P2 in thecharacteristic curve 21.

When the first light-emitting element 109 and the second light-emittingelement 110 emit light of different wavelengths at different scatteringangles, the resulting scattering efficiency is as described above. Then,the amount of received light of the light-receiving element 111 can berepresented as (amount of received light)=(amount of emittedlight)×(light-received efficiency), whereby the amount of light-receivedsignal is in direct proportion to the scattering efficiency I of FIG.23.

In the third embodiment, ratio R is found; the ratio R is the ratio ofthe amount of light received by the light-receiving element 111 when thelight emitted from the first light-emitting element 109 is scattered bysmoke to the amount of light received by the light-receiving element 111when the light emitted from the second light-emitting element 110 isscattered by the same type of smoke. Since the ratio R of the amount ofreceived light is in direct proportion to the scattering efficiency,when the scattering efficiency is represented as A1 and A2, R can befound as R=A1/A2. Through the comparison of the ratio R with thepredetermined threshold, the type of the smoke can be decided.

FIG. 24 is a graph of the scattering efficiency I against the scatteringangle θ, which is obtained when the light emitted from the firstlight-emitting element 109 and the light emitted from the secondlight-emitting element 110 are scattered by the combustion smoke (blacksmoke) generated by the combustion of kerosene when the smoke-sensingunit has the configuration shown in FIGS. 16 to 21.

In FIG. 24, when the light emitted from the first light-emitting element109 has the first wavelength λ1=900 nm, the scattering efficiency I ofthe light can be represented as a characteristic curve 22. On the otherhand, when the light emitted from the second light-emitting element 110has the second wavelength λ2=500 nm, the scattering efficiency I of thelight can be represented as a characteristic curve 23.

When the wavelength is focused in the graph of FIG. 24, similarly to thesmoke of cotton lampwick of FIG. 23, the characteristic curve 22 takeslow values, whereas the characteristic curve 23 takes higher values,wherein the characteristic curve 22 shows the scattering efficiency ofthe light emitted from the first light-emitting element 109 and thelight has the first wavelength λ1=900 nm, and the characteristic curve23 shows the scattering efficiency of the light emitted from the secondlight-emitting element 110 and the light has the shorter secondwavelength λ2=500 nm.

Further, the variation in the scattering efficiency against thescattering angle θ is similar to the case of FIG. 23. In both thecharacteristic curves 22 and 23, the scattering efficiency becomes highas the scattering angle θ decreases. The scattering efficiency hits theminimum value when the scattering angle θ is approximately 120°, thenthe scattering efficiency increases along with the increase in thescattering angle θ.

With respect to the combustion smoke of kerosene, when the firstscattering angle θ1 of the first light-emitting element 109 is 300 inthe characteristic curve 22, the scattering efficiency is A1′ at pointP3. Further, with respect to the second light-emitting element 10, sincethe second scattering angle θ2 is 120°, the scattering efficiency is A2′at point P4 in the characteristic curve 23.

Similarly to the case of FIG. 23, the scattering efficiencies A1′ andA2′ is in direct proportion to the amount of received light, i.e.,product of the amount of emitted light and the light-receivedefficiency. Hence, the ratio R, which is the ratio of the amount oflight emitted from the first light-emitting element 109 and received bythe light-receiving element 111 to the amount of light emitted from thesecond light-emitting element 110 and received by the light-receivingelement 111, is found as R=A1′/A2′ based on the scattering efficienciesA1′ and A2′.

FIG. 25 shows a list of the amount of light-received signal A1 for thefirst light-emitting element 109, the amount of light-received signal A2for the second light-emitting element 110, and the ratio R of the amountof signals, with respect to the fumigation smoke of the cotton lampwickand the combustion smoke of the kerosene, by way of example. Here, sincethe amount of light-received signal is in direct proportion to thescattering efficiency, the values of the scattering efficiency I ofFIGS. 23 and 24 are shown as they are.

As is clear from the list of FIG. 25, with respect to the fumigationsmoke, which appears to be white smoke, generated by the combustion ofthe cotton lampwick, the ratio R of the amount of light-received signalsfor the light from the first light-emitting element 109 and the lightfrom the second light-emitting element 110 is 8.0.

On the other hand, with respect to the combustion smoke, which appearsto be black smoke, generated by the combustion of kerosene, the ratio Rof the amount of light-received signals for the light from the firstlight-emitting element 109 and the light from the second light-emittingelement 110 is 2.3.

Hence, with respect to the white fumigation smoke and the blackcombustion smoke, there is a sufficient difference between the ratios ofthe amounts of light-received signals for the light from the firstlight-emitting element 109 and for the light from the secondlight-emitting element 110. If the ratio R is to be employed as athreshold for deciding the type of the smoke, the threshold may be setto 6, so that the smoke generated at the fire occurrence can be decidedto be the fumigation smoke or the combustion smoke.

On the other hand, the water vapor or the steam have sufficiently largerparticle diameter compared with the smoke particle. Hence, thescattering efficiency is sufficiently higher than that of the smoke fromfire when the scattering angle θ is small in FIGS. 23 and 24, and theamount of light-received signal for the light from the firstlight-emitting element 109 at the first scattering angle θ1 issufficiently large, so that the ratio R of the amount of light-receivedsignal for the light from the first light-emitting element 109 at thefirst scattering angle θ1 to the amounts of light-received signal forthe light from the second light-emitting element 110 at the secondscattering angle θ2=120° takes a large value of 10 or more.

Hence, it is possible to set the threshold to 10 with respect to theratio R of the amount of light-received signal for the light from thefirst light-emitting element 109 to the amount of light-received signalfor the light from the second light-emitting element 110, and to decidethat the smoke is not from fire but from water vapor or steam when theratio R is above the threshold.

The same applies to the smoke of tobacco. Since the ratio R is 10 ormore for the smoke of tobacco, if the threshold for the ratio R is setto 10, and the ratio is above the set threshold, smoke can be similarlydecided as being caused by non-fire.

FIG. 26 is a flowchart of the fire sensing process by sensor with thecircuit block of FIG. 19 having the smoke-sensing unit of FIGS. 16 to21, and the fire sensing process is realized by programmed control ofCPU which functions as the signal processing unit 103.

In the fire sensing process, only the first light-emitting element 109is driven to emit light in the normal operation. When the level ofreceived light from the first light-emitting element 109 exceeds apredetermined threshold which serves like a pre-alarm, the sensor drivesthe second light-emitting element 110 to emit light and decides whetherthe fire occurs or not based on the ratio of the amounts of receivelight signals for the light from the first light-emitting element 109and for the light from the second light-emitting element 110.

In FIG. 26, first the counter n is set as n=1 in step SB1. Then, in stepSB2, the first light-emitting element 109 is driven to emit light likepulses. In step SB3, in response to the light emission driving of thefirst light-emitting element 9, the light-received signal of thelight-receiving element 111 is sampled and held, and light-received dataA1 is stored in the storing unit 104. Simultaneously, the differentialvalue B is found for the light-received data A1 and stored in thestoring unit 104.

The first light emission controlling unit 105 of FIG. 19, similarly tothe first embodiment shown in FIG. 6, performs modulated light emissionby driving the first light-emitting element 109 to emit light aslight-emission pulses so that pulse width T2 is output repeatedly everycycle T1. Accordingly the amplifying circuit 107 takes in thelight-received signal as a synchronous light-received signal which is insynchronization with the light emission modulation.

The light-emission cycle T1 is, for example, 1 second, and the pulsewidth T2 of the modulated light emission is, for example, 500microseconds. The modulated light emission and corresponding synchronouslight reception allow for the elimination of light-received signalgenerated by the incidence of light other than the scattered light bythe smoke in the smoke-sensing space outside, and secure the receptionof only the scattered light of the smoke.

Further, since the light emission wavelength band of the firstlight-emitting element 109 is in a visible light band, the lightemission time period is restricted to 1 millisecond or less so that thehuman cannot visually recognize the intermittently emitted light. Forthe human to visually recognize the light from the light-emittingelement, the light emission must continue for more than 1 millisecond.Hence, the light emission time period is restricted to 1 millisecond orless so that the human cannot visually recognize the light from thelight-emitting element.

In case of the modulated light-emission pulse, it is sufficient if thetotal light emission time period of three light-emission pulses is 1millisecond or less. In this case the total light emission time periodis 150 microseconds, so that the light emission is not visuallyrecognized. The modulated light emission and the synchronous lightreception are similar for the light emission control of the secondlight-emitting element 110 by the second light emission controlling unit106 of FIG. 19.

Returning again to FIG. 26, it is checked whether the light-receiveddata A1 exceeds the predetermined threshold TH1 or not in step SB4, thepredetermined threshold TH1 serves for judgment on a pre-alarm of thefire. When the light-received data A1 exceeds the threshold, theobstacle judgment process of step SB5 described later is performed. Whenthe smoke is decided as not from non-fire, the second light-emittingelement 110 is driven to emit light as pulses in step SB6, and thelight-received signal obtained from the light-receiving element 110 issampled and held in step SB7, and stored as light-received data A2 inthe storing unit 104.

Then, the ratio R is calculated in step SB8, wherein the ratio R is theratio of the light-received data A1 for the light from the firstlight-emitting element 109 stored in the storing unit 104 to thelight-received data A2 for the light from the second light-emittingelement 110 stored in the storing unit 104. Then, the ratio R iscompared with the predetermined threshold=10 for deciding whether thesmoke is from non-fire or not in step SB9. When the ratio R is smallerthan the threshold=10, the smoke is decided as from fire, and the ratioR is compared with the threshold=6 for deciding the type of thecombustion material in step SB10.

Here, if the ratio R is equal to or more than the threshold=6, the firecausing the smoke is decided to be the white smoke fire (fumigationfire) in step SB11. In step SB12, the count n of the counter isincremented by one, and in step SB13 it is checked whether the count nof the counter reaches 3 or not.

Since the count n of the counter is 2, the process returns to step SB2,to repeat the process from step SB2 to SB12. When the count n of thecounter reaches 3 in step SB13, the smoke is decided to be from fire instep SB15. Then the fire signal is sent. If necessary, informationindicating that the fire is white smoke fire is sent simultaneously.

On the other hand, when the ratio R is less than the threshold=6 in stepSB10, the process proceeds to step SB14, and the smoke is decided to befrom the black smoke fire (combustion fire). In step SB15 the smoke isdecided to be from fire and the fire signal is sent to the receiverside. If necessary, the information indicating that the fire is blacksmoke fire is sent simultaneously. When the ratio R is equal to orhigher than the threshold 10 in step SB9, the smoke is decided to befrom non-fire in step SB16, and the process returns to step SB1. Thecounter is reset to n=1.

Thus, in the third embodiment, lights with different wavelengths anddifferent scattering angles are emitted from the first light-emittingelement 9 and the second light-emitting element 10 in the smoke-sensingunit of FIGS. 16 to 21. The lights are received by the light-receivingelement 11 and the ratio of the two is found and compared with thepredetermined threshold. Based on the comparison, it is decided whetherthe smoke is from fire or from non-fire. Further, when the smoke isdecided to be from fire, the type of the combustion material, i.e.,whether the fire is the white smoke fire or the black smoke fire can besurely decided.

Here, in the smoke-sensing unit with the configuration of FIGS. 16 to21, the first wavelength λ1 is set to 900 nm, and the first scatteringangle θ1 is set to 300 for the first light-emitting element 109, and thesecond wavelength λ2 is set to 500 nm, and the second scattering angleθ2 is set to 120° for the second light-emitting element 110, by way ofexample. In the third embodiment, though the optimal values are asabove, the values of the following range can realize the same effect.

First, the first wavelength λ1 of the first light-emitting element 109may have a central wavelength of 800 nm or more. The first scatteringangle θ1 of the first light-emitting element 109 may be in the range ofθ1=20° to 50°. On the other hand, the second wavelength λ2 of the secondlight-emitting element 110 may have the central wavelength of 500 nm orless, and the second scattering angle θ2 may be in the range of θ2=100°to 150°.

More specifically, the first wavelength λ1 and the scattering angle θ1of the first light-emitting element 109 and the second wavelength λ2 andthe scattering angle θ2 of the second light-emitting element 110 may beset so that the ratio R of the amounts of received light from respectiveelements is higher than the threshold=6 for distinction of thecombustion material with respect to the smoke of the cotton lampwick ofFIG. 23, i.e., the fumigation smoke (white smoke), whereas the ratio Rof the amount of received light, i.e., the ratio of light emitted by thefirst light-emitting element 109, scattered by the smoke, and receivedto the amount of light emitted by the second light-emitting element 110,scattered by the smoke, and received, may be set smaller than thethreshold=6 with respect to the combustion smoke of kerosene of FIG. 25,i.e., the combustion smoke (black smoke).

Further, in the signal processing unit 3 of FIG. 19, inherent falsealarm caused by the setting of the smoke-sensing point P in the opensmoke-sensing space outside the outer surface 118 of the sensor body isdistinguished and the obstacle signal is output.

The inherent false alarm caused by the setting of the smoke-sensingpoint P outside is, for example, expected to be generated by the foreignsubstances, such as the person's hand or the insects, directly passingover the smoke-sensing point P. Hence in the process of FIG. 26, theobstacle judgment process is provided in step SB5, and the content ofthe processing is as shown in the flowchart of FIG. 27.

In the obstacle judgment process of FIG. 27, first it is checked whetherthe differential value B of the light-received data A1 exceeds thepredetermined obstacle threshold TH2 or not in step SC1. When thedifferential value B does not exceed the predetermined obstaclethreshold TH2, the process proceeds to step SB6 of FIG. 26, and the firejudgment process is performed.

When the differential value B exceeds the obstacle threshold TH2, thepredetermined time T is set to the timer and the timer starts in stepSC2. In step SC3, the elapse of the set time T is monitored. When theset time T has elapsed, the process proceeds to step SC4, and it ischecked whether the light-received data A1 at the time exceeds theobstacle threshold TH3 or not. When the light-received data A1 exceedsthe obstacle threshold TH3, it is decided that the foreign substancessuch as spider's nest adheres to the smoke detecting portion of theouter surface 118 of the sensor body, and the presence of trouble isnotified as an output in step SC5. Then, the receiver makes the displayindicating the obstacle, so as to prompt the maintenance check, such ascleaning, of the outer surface of the sensor body.

Similarly to FIG. 8 of the first embodiment, the increase in the smokeconcentration by the fire is relatively mild. Hence, the differentialvalue B is sufficiently small compared with the false alarm thresholdTH2, and does not exceeds the false alarm threshold TH2 when fireoccurs. Therefore, when the light-received data A1 exceeds the pre-alarmthreshold TH1 at time t1, the differential value B is lower than thefalse alarm threshold TH2, which is decided in step SC1 of FIG. 27.Then, the obstacle judgment process of steps SC2 to SC5 is skipped, andthe process proceeds to the fire judgment process after step SB6 of FIG.26. Here, the obstacle threshold TH3 is set at a sufficiently high levelcompared with the pre-alarm threshold TH1 for fire judgment.

FIG. 28 shows a case where a foreign substance such as an insecttemporarily passes over the portion of the smoke-sensing point P in theoutside open space outside the outer surface 118 of the sensor body. Thelight-received data A1 changes so as to temporarily exceed the obstaclethreshold TH3. Along with the change in the light-received data A1, thedifferential value B changes to a positive direction so as to exceed thefalse alarm threshold TH2 at the rising of the light-received data A1,and further the differential value B changes significantly to a negativedirection at the falling of the light-received data A1.

A predetermined value B which is stored immediately before the time thelight-received data A1 exceeds the obstacle threshold TH3 is comparedwith the false alarm threshold TH2. When the predetermined value Bexceeds the false alarm threshold TH2, it is decided that there is apossibility of obstacle. In order to check the subsequent changes, thetimer is activated when the differential value B exceeds the obstaclethreshold TH2, and the sensor stands by until the set time T elapses.

Then, the light-received data A1 is checked again after time T elapses.Since the light-received data A1 is equal to or less than the obstaclethreshold TH3, the obstacle is decided to be temporal. Since theobstacle is already removed, no output is provided to indicate theobstacle. In other words, the execution of the fire judgment process issuppressed.

FIG. 29 shows a case where a relatively large foreign substance such asa large insect adheres to and sticks to the outer surface 118 of thesensor body near the smoke-sensing point P in the outside open space.The light-received data A1 changes so as to exceed the obstaclethreshold TH3, and remains at the level. Accordingly, the differentialvalue B changes significantly to a positive direction so as to exceedthe obstacle threshold TH2 at the rising of the light-received data A1.

A differential value B which is stored immediately before the time thelight-received data A exceeds the obstacle threshold TH3 is comparedwith the false alarm threshold TH2. When the differential value Bexceeds the false alarm threshold TH2, it is decided that there is apossibility of an obstacle. In order to check the subsequent changes,the timer is activated when the differential value B exceeds theobstacle threshold TH2, and the sensor stands by until the set time Telapses. Then, the light-received data A1 is checked again after time Telapses. Since the light-received data A exceeds the obstacle thresholdTH3 at this time, the obstacle is decided to be continuous, and theoutput is supplied to indicate the presence of obstacle.

Thus, the smoke sensor according to the third embodiment, in addition toexerting the similar effect as the second embodiment, allows multipledecisions to be made based on the plural pieces of data on the amount ofreceived light, whereby the fire sensing can be even more accuratelyperformed.

Further, since the scattering characteristics are made different by thewavelengths, and the combined effect of the differences in thescattering angles and the wavelengths creates a significant differencein the light intensity of the scattered light depending on the type ofthe smoke, whereby the types of the smoke can be more accuratelydistinguished.

Further, since the plural light-emitting elements are arranged atsolid-angle, the smoke-sensing point, which is a crossing point of thelight axis of the light-emitting element and the light axis of thelight-receiving element, can be set in a space outside the outer surfaceof the sensor body for the sensing of the light scattered by the smoke.

Further, since the amount of received scattered light generated from thelight from the first light-emitter and the amount of received scatteredlight generated from the light from the second light-emitter arecompared, it is possible to find the ratio of the two and compare theobtained ratio with the threshold. Thus, the type of the smoke can beidentified so as to allow for more accurate fire sensing.

Further, since the light-receiving element is set to have the angle offield of view of 5 degrees or less, the size of the area for the sensingof scattered light in the smoke-sensing space can be set to a requisiteminimum, whereby the influence by the outside light can be prevented.

Further, since the light-emitting element emits collimated parallelbeam, the size of the area for the sensing of scattered light in thesmoke-sensing space can be set to a requisite minimum, whereby theinfluence by the outside light can be prevented.

Next, a fourth embodiment will be described. Though the fourthembodiment is configured basically similarly to the third embodiment,the fourth embodiment is different from the third embodiment in that thescattering angle and the direction of polarization of the twolight-emitting elements are different from those in the thirdembodiment. The configuration and the method of the fourth embodimentis, if not particularly specified otherwise, similar to those of thethird embodiment, and the components with the same functions arereferred to by the same name or denoted by the same reference charactersas the third embodiment.

FIG. 30 schematically describes the configuration of a smoke-sensingunit of the fourth embodiment. In FIG. 30, a first light-emittingelement 125, a second light-emitting element 129, and a light-receivingelement 133 are arranged so as to face the smoke-sensing point P whichis the light axis crossing point. The smoke-sensing point P is locatedin the outside space of the smoke sensor.

The first light-emitting element 125 emits light 128 which has thevertical polarization plane which is vertical to a first scatteringplane 127, which is a plane passing through a light axis 125A of thefirst light-emitting element 125 and a light axis 133 a of thelight-receiving element 133.

In the present example, the LED is employed as the first light-emittingelement 125. Hence, a polarization filter 126 is arranged in front ofthe first light-emitting element 125, so that emitted light 128 has thevertical polarization plane to the first scattering plane 127. The firstscattering angle θ1 formed by the light axis 125 a of the firstlight-emitting element 125 in the first scattering plane 127 and thelight axis 133A of the light-receiving element 133 is set, for example,to 70°.

On the other hand, the second light-emitting element 129 emits lights132 which has a parallel polarization plane to a second scattering plane131 which is a plane passing through a light axis 129 a of the secondlight-emitting element 129 and the light axis 133A of thelight-receiving element 133. Further, the second scattering angle θ2formed by the light axis 129 a of the second light-emitting element 129and the light axis 133 a of the light-receiving element 133 on thesecond scattering plane 131 is set to a larger angle than the firstscattering angle θ1, for example θ2=120°.

Since the LED is employed for the second light-emitting element 129 aswell, a polarization filter 130 is arranged in front of the secondlight-emitting element 129, so that emitted light 132 has the parallelpolarization plane.

Since the light 128 emitted from the first light-emitting element 125has the vertical polarization plane to the first scattering plane 127,and the light 132 emitted from the second light-emitting element 129 hasthe parallel polarization plane to the second scattering plane 131, thelight scattered at the point P and directed to the light-receivingelement 133 become light 134 having the parallel polarization plane tothe second scattering plane 131 and directed onto the smoke particles.

The three-dimensional arrangement of the configuration of thesmoke-sensing unit according to the fourth embodiment, as shown in FIG.31, includes the first light-emitting element 125, the secondlight-emitting element 129, and the light-receiving element 133 arrangedat solid angles and embedded into the chamber base 114 (not shown)similar to the third embodiment. The smoke-sensing point P which is thelight axis crossing point is set in the outside space at the height h ofapproximately 5 mm from the outer surface 118 of the sensor body.

Specifically, if the positions of the first light-emitting element 125,the second light-emitting element 129, and the light-receiving element133 are represented as A, B, and C, respectively, as shown in FIG. 31,these points A, B, and C are arranged so that a triangle formed by threepoints A, B, C, is a base of a trigonal pyramid whose apex is thesmoke-sensing point P, i.e., the light axis crossing point, which islocated in the outside space of the outer surface of the chamber base114.

FIG. 32A shows the solid-angle arrangement of the first light-emittingelement 125, the second light-emitting element 129, and thelight-receiving element 133, with respect to the light axes 25 a, 29 a,and 33 a thereof.

The smoke-sensing point P which is a crossing point of the light axes125 a, 129 a, and 133 a of the first light-emitting element 125, thesecond light-emitting element 129, and the light-receiving element 133is located in the smoke-sensing space outside the outer surface 118 ofthe sensor body in the chamber base 114 shown in FIGS. 16 to 18. On theother hand, the first light-emitting element 125, the secondlight-emitting element 129, and the light-receiving element 133 arearranged in the chamber base 114.

FIG. 32B shows the solid-angle arrangement of the point A of the firstlight-emitting element 125 and the point C of the light-receivingelement 133. Here, a plane including the light axes 125 a and 133 a fromthe point A of the first light-emitting element 125 and the point C ofthe light-receiving element 133 is given as the triangle PCA, and anangle formed by the light axis 125 a and the light axis 133 a on theplane including the triangle PCA is the first scattering angle θ1 of thefirst light-emitting element 125.

FIG. 32C shows the solid-angle arrangement of the point B of the secondlight-emitting element 129 and the point C of the light-receivingelement 133. Here, the light axes 129 a and 133 a are present in theplane including the triangle PCB, and a scattering angle formed by thelight axis 129 a of the second light-emitting element 129 and the lightaxis 133 a of the light-receiving element 133 is given as the secondscattering angle θ2 formed by the light axis 129 a and the light axis133 a on the plane including the triangle PCB.

FIG. 33 is a list of experimental results of the amount oflight-received signal depending on the types of smoke when thescattering angle and the polarization angle are changed in thesmoke-sensing unit with the configuration of FIG. 30. In FIG. 33, thescattering angle θ is 700, 900, 1200, and the polarization angle φ isset to 0° (horizontal polarization) and 900 (vertical polarization) foreach value of the scattering angle θ.

Here in the fourth embodiment, the similar process (FIGS. 26 and 27) isperformed by the circuit block (FIG. 19) similar to that in the thirdembodiment, for the decision on the presence of fire and obstacle.Further, the threshold for deciding whether the smoke is from non-fire,the threshold for deciding whether the fire is the white smoke fire orthe black smoke fire can be the same as in the third embodiment.

FIG. 33 shows the amount of light-received signal for each of the casewhere the light emitted from the first light-emitting element 125 andthe second light-emitting element 129 is scattered by the combustionsmoke of the filter paper, kerosene, and tobacco. When the amount of thelight-received signal of FIG. 33 is examined with respect to thescattering angle θ and the polarization angle φ, the following can beseen.

First, with regards to the variation in the scattering angle θ, theamount of the light-received signal increases as the scattering angledecreases, whereas the amount of the light-received signal decreases asthe scattering angle increases, for both the vertically polarized lightof the first light-emitting element 125, and the parallel polarizedlight of the second light-emitting element 129.

On the other hand, when the values are examined for the same scatteringangle θ, for example, 70°, the amount of light-received signal for thevertically polarized light of the first light-emitting element 125 islarger than the amount of light-received signal for the parallelpolarized light of the second light-emitting element 129.

At the fire judgment, the ratio R of the amount of light-received signalA1 for the light from the first light-emitting element 125 to the amountof light-received signal A2 for the light from the second light-emittingelement 129 is calculated as R=A1/A2, and it is decided whether thesmoke is of fire or non-fire, and if the smoke is from fire, whether thefire is the white smoke fire or the black smoke fire.

To increase the ratio R, the scattering angle θ1=70°, which is small soas to increase the amount of light-received signal, is selected for thefirst light-emitting element 125, while the scattering angle θ2=120°,which makes the amount of light-received signal decrease, is selectedfor the second light-emitting element 129.

On the other hand, when the scattering angle is the same, the amount oflight-received signal is larger for the vertically polarized light, andsmaller for the parallel polarized light. To obtain a large ratio R, thevertical polarization with the polarization angle φ1=90° is selected forthe first light-emitting element 125 to increase the amount oflight-received signal, and parallel polarization with the polarizationangle φ2=0° is selected for the second light-emitting element 129 todecrease the amount of light-received signal.

Based on the measurement results for the scattering angle θ andpolarization angle φ as shown in FIG. 33, in the embodiment of FIG. 31,(1) the first light-emitting element 125 is set so as to have thevertical polarization with the first scattering angle θ1=70°, and (2)the second light-emitting element 129 is set so as to have the parallelpolarization with the second scattering angle θ2=120°.

FIG. 34 shows a list of the amount of light-received signal A1 for thelight from the first light-emitting element 125 and the amount oflight-received signal A2 for the light from the second light-emittingelement 129 depending on the types of the combustion material when thepolarization direction and the scattering angle are set as (1) and (2)above. Further, the ratio R of the two amounts of light-received signalis calculated and shown.

As is clear from the list of FIG. 34, for the combustion material at thefire, such as the filter paper and kerosene, the ratio R is 4.44, 5.60and small, whereas for the tobacco which is categorized as non-fire, theratio R is 16.47 and sufficiently large. Hence, as shown in theflowchart of FIG. 26, decision based on the ratio R and the threshold=10in step SB9 allows for the secure distinction between the fire andnon-fire.

Further, since the smoke generated by the combustion of kerosene of FIG.34 belongs to the black smoke fire, with the use of the threshold=6 instep SB10 of FIG. 26, it can be decided that it is black smoke fire(combustion fire) in step SB14.

The smoke generated by the fumigation of the cotton lampwick shown inFIG. 23 is not shown in FIG. 34. However, the ratio R thereof isnecessarily larger than the value for kerosene. Hence, the ratio R isequal to or larger than the threshold=6 in step SB10 of FIG. 26, thesmoke is decided to be from the white smoke fire in step SB10, and whenthe counter n reaches the count of three, it is decided that the fireoccurs.

In the embodiment of FIG. 30, the first scattering angle θ1=70° of thefirst light-emitting element 125 is set as an example. Practically, θ1is set to a value equal to or lower than 80°. Further, the secondconfiguration angle θ2 of the second light-emitting element 129 is setto 1200 as an example. Practically, (θ2 may be set to a value equal toor higher than 100°.

Thus, in addition to exerting the same effect as the third embodiment,the fourth embodiment has the following effect. The scatteringcharacteristic is made different by the polarization direction of thelight, and at the same time the scattering angles of the light-receivingelements in two light-emitting units are made different. Thus, thescattering characteristic is made different for each type of smoke, andaccuracy in smoke identification can be improved.

A fifth embodiment will be described. When the smoke-sensing point isset outside the light scattering type smoke sensor, the smoke does notstay inside the smoke chamber as in the conventional smoke sensor,whereby the concentration of the smoke can be more accurately reflectedin the fire sensing. The fifth embodiment is characterized in that theprocessing is performed for more accurate sensing of fire with the useof such characteristic. The configuration and the method of the fifthembodiment are, if not specifically described otherwise, similar tothose of the first embodiment, and the components with the samefunctions are referred to by the same name, or denoted by the samereference characters as in the first embodiment.

In the fifth embodiment, the light scattering type smoke sensor isconfigured as shown in FIG. 1, and the basic electric configurationthereof is as shown in FIG. 5. In the fifth embodiment, a first firethreshold TH1 and a second fire threshold TH2 are set as the thresholdsfor fire sensing. The first fire threshold TH1 and the second firethreshold TH2 are stored in the storing unit 17 in advance by anoptional manner. The first fire threshold TH1 serves to indicate thatthe smoke concentration in the monitoring area reaches a level which ishigher than a normal time (clean air time) and indicates possibility offire occurrence though not high enough to allow for determination offire occurrence. The second fire threshold TH2 is set to a higher levelthan the first fire threshold TH1 (second fire threshold TH2>first firethreshold TH1), and indicates that the smoke concentration in themonitoring area is higher than the normal time (clean air time) andallows for determination of fire occurrence.

In the fifth embodiment, the elapse of time since the fire sensing levelexceeds the first fire threshold TH1 is judged based on a first set timeTA1 as a standard for judgment, whereas the elapse of time since thefire sensing level exceeds the second fire threshold TH2 is judged basedon a second set time TA2 as a standard for judgment. The first set timeTA1 and the second set time TA2 are stored in the storing unit 17 by anoptional manner in advance.

Next, a fire decision process in the fifth embodiment will be described.FIG. 35 is a flowchart of the fire judgment process. First in step SD1,it is checked whether the amount of received light A is lower than thefirst fire threshold TH1 or not. When the amount of received light Aexceeds the first fire threshold TH1, the process proceeds to step SD2,where the counting of the first set time TA1 starts. After the countingstarts, the elapse of the first set time TA1 is checked in step SD3.Meanwhile, whether the amount of received light A remains at a levelequal to or higher than the first fire threshold TH1 or not iscontinuously monitored in step SD4. When the amount of received light Abecomes lower than the first fire threshold TH1 before the first settime TA1 elapses, it is decided that the smoke concentration risesmerely temporarily due to causes other than fire. In this case, noparticular output is given to indicate fire decision.

On the other hand, when the amount of received light A remains to be ata level equal to or higher than the first fire threshold TH1 until thefirst set time TA1 elapses, the process proceeds to step SD5, where theelapse of the second set time TA2 is monitored. Meanwhile, it iscontinuously monitored whether the amount of received light A becomesequal to or higher than the fire threshold TH2 or not. When the amountof received light A becomes lower than the fire threshold TH2 before thesecond set time TA2 elapses, it is decided that the smoke concentrationrises merely temporarily due to causes other than fire. In this case, noparticular output is given to indicate fire decision. On the other hand,when the amount of received light A remains to be equal to or higherthan the second fire threshold TH2 after the second set time TA2elapses, it is decided that the fire occurs, and output is given toindicate fire decision in step SD7.

A background, an effect, or the like for the above described processingwill be described. The conventional light scattering type smoke sensordetects fire by introducing the smoke inside the smoke chamber. Hence,it takes time until the smoke flows into the smoke chamber, which maycause delay in fire sensing. Further, once the smoke enters the smokechamber, it takes time until the smoke flows out from the smoke chamber.Then, even when the smoke concentration outside the smoke chamber isalready low, the smoke concentration inside the smoke chamber remainshigh, which can induce false alarm.

For example, in the conventional light scattering type smoke sensorprovided with the smoke chamber, the changes in the smoke concentrationof the smoke of the fire tends to resemble to the changes in the smokeconcentration of the smoke generated by causes other than fire (e.g.,tobacco or cooking). In other words, though the smoke concentration ofthe smoke of the fire tends to keep rising by nature, the smokeconcentration of the smoke by tobacco, cooking, or the like tends tofluctuate. Particularly, when the smoke concentration becomes low, thelevel becomes extremely lower than the level of the smoke concentrationof the smoke of the fire. Such difference in variations in smokeconcentration is detected merely as a minor difference in theconventional light scattering type smoke sensor provided with the smokechamber.

FIG. 36 shows a relation between light-received level and time withrespect to the smoke of tobacco in the conventional light scatteringtype smoke sensor provided with the smoke chamber. FIG. 37 shows arelation between the light-received level and time with respect to thesmoke of the fire in the conventional light scattering type smoke sensorprovided with the smoke chamber. Further, FIG. 38 shows a relationbetween the light-received level and time with respect to the smoke oftobacco in the light scattering type smoke sensor of the fifthembodiment. FIG. 39 shows a relation between the light-received leveland time with respect to the smoke of the fire in the light scatteringtype smoke sensor of the fifth embodiment. In FIGS. 36 to 39, thehorizontal axis represents time, and the vertical axis representslight-received level.

First, when the light-received level for the smoke of tobacco shown inFIG. 36 is compared with the light-received level for the smoke of fireshown in FIG. 37, it can be seen that though the fluctuation is slightlylarger in the light-received level for the smoke of tobacco, the graphsshow generally similar transitions. Such similarity comes from the factthat since the inflow and outflow of the smoke to/from the smoke chambertake time, the smoke tends to stay inside the smoke chamber and thelight-received level is equalized. Hence, mutual differentiation of thesmoke of tobacco and the smoke of fire is difficult to achieve based onsuch light-received level.

On the other hand, when the light-received level for the smoke oftobacco shown in FIG. 38 is compared with the light-received level forthe smoke of fire shown in FIG. 39, the fluctuation is larger in thelight-received level for the smoke of tobacco, which marks notabledifference from the light-received level for the smoke of fire. In thefifth embodiment, the fire is distinguished from the non-fire throughthe processing as shown in FIG. 35 focusing such point.

According to the process shown in FIG. 35, even when the light-receivedlevel exceeds the first threshold TH1 due to the generation of smoke oftobacco (time T1 of FIG. 38), if the light-received level becomes lowerthan the first threshold TH1 (time T2 of FIG. 38) before the first settime TA1 elapses, the sensor does not decide that the fire occurs.Further, even when the light-received level exceeds the first thresholdTH1 (time T3 of FIG. 38) and further exceeds the second threshold TH2(time T4 of FIG. 38), if the light-received level becomes lower than thesecond threshold TH2 before the second set time TA2 elapses (time T5 ofFIG. 38), the sensor does not decide that the fire occurs. In brief,even if the light-received level becomes high, if such state does notcontinue for a predetermined time period, the sensor decides that thesmoke is caused by non-fire, and does not raise fire alarm, wherebyfalse alarm can be prevented.

On the other hand, when the smoke is generated from the fire, and thelight-received level exceeds the first threshold TH1 (time T1 of FIG.39) and remains higher than the first threshold TH1 even after the firstset time TA1 elapses (time T2 of FIG. 39), and further, if thelight-received level exceeds the second threshold TH2 (time T3 of FIG.39) and such state continues even after the second set time TA2 elapses(time T4 of FIG. 39), the sensor raises fire alarm.

Specifically, the first threshold TH1, the second threshold TH2, thefirst set time TA1, and the second set time TA2 can take any values, andmay be determined based on the results of experiments or the like. Forexample, the first set time TA1 may be set to 30 seconds, and the secondset time TA2 may be set to 60 seconds.

Thus, in addition to the same effect obtained in the first embodiment,the fifth embodiment utilizes the feature that the different tendenciesin behaviors of the smoke of fire and non-fire can be directly reflectedin the sensing result, thereby exerting an effect that the smoke fromfire and non-fire can be distinguished from each other, and allows forthe prevention of the false alarm.

Hereinabove, the first to the fifth embodiments are described.Advantages and variations other than those described above may bereadily deduced by those skilled in the art. Hence, the presentinvention in its broad sense is not limited to the details and therepresentative embodiments shown herein. In other words, variousmodifications can be made within the concept and the scope of thepresent invention as defined by the appended claims and theirequivalents.

For example, features of the first to the fifth embodiments may bemutually adoptable. For example, the processing with the first and thesecond fire threshold TH1 and TH2 as in the fifth embodiment may beincorporated into the light scattering type smoke sensor provided withplural light emitters as in the third embodiment.

Further, on the surface of the outer surface 7 of the sensor body of thefirst embodiment, an uneven screen may be attached to prevent theadherence of insects or foreign substances in a way that the screen doesnot protrude by a notable amount compared with other parts. In the firstembodiment, the transparent cover 9 is attached so as to cover theentire outer surface 7 of the sensor body. The protective cover 9,however, may be arranged only on the light-emitting opening 5 b and thelight-receiving opening 6 b. Further, since the outer surface 7 of thesensor body faces downwards when the smoke sensor is installed on theceiling, the smoke sensor may be configured as an open-type sensor inwhich the transparent cover 9 is not attached to the light-emittingopening 5 b and the light-receiving opening 6 b.

In the fourth embodiment of FIG. 30, the LED is employed as the firstlight-emitting element 125 and the second light-emitting element 129,and combined with the polarization filters 126 and 130, respectively, sothat the first light-emitting element 125 emits light 128 with verticalpolarization plane and the second light-emitting element 129 emits light132 with parallel polarization plane. The polarization filters 126 and130 may become unnecessary, however, if a laser diode emitting polarizedlight is employed as the first light-emitting element 125 and the secondlight-emitting element 129 instead.

In the fourth embodiment, the wavelengths of the first light-emittingelement 125 and the second light-emitting element 129 are made equal.However, the accuracy in smoke identification may be further enhancedwhen the wavelengths are made different.

As shown in FIGS. 16 to 21, the wavelengths and the scattering angles oftwo light-emitting elements are made different in the smoke-sensingunit. As an alternative embodiment, two light-receiving elements may beprovided for two light-emitting elements 109 and 110 as far as therelation of the wavelengths and the scattering angles of the firstlight-emitting element 109 and the second light-emitting element 110 aremaintained.

Still alternatively, a light-emitting element with wider emissionspectrum, such as incandescent lamp or white LED may be employed as thelight-emitting element, so that only one light-emitting element issufficient. Then, the optical paths are arranged by provision of awavelength-switching filter to the light-emitting element, so that thelight is emitted from positions corresponding to the firstlight-emitting element 109 and the second light-emitting element 110shown in FIG. 16.

The smoke-sensing unit is configured so that the two light-emittingelements 125 and 129 have different scattering angles and polarizationdirections in FIG. 30. Alternatively, two separate light-receivingelements may be provided at different positions respectively for the twolight-emitting elements 125 and 129 with different polarization planes.

The polarization planes of light emitted from two light-emittingelements 125 and 129 may be adjusted as appropriate to optimize thedetecting state. For the adjustment, the polarization filters 126 and130 of FIG. 30 may be mechanically rotated, or the polarization planes128 and 132 may be changed through the driving of a known liquid crystalfilter, so that the polarization direction of the polarization plane 134is properly adjusted.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing, the light scattering type smokesensor according to the present invention is useful for sensing smoke tonotify the occurrence of fire, and particularly suitable for building asmoke sensing system with a good appearance by reducing the amount ofprotrusion of the light scattering type smoke sensor from the installedsurface such as a ceiling surface, and for giving an accuratenotification of fire by distinguishing different types of smoke fromeach other.

1. A light scattering type smoke sensor comprising: a sensor body; alight-emitter that is incorporated in the sensor body to emit lighttoward an open smoke-sensing space located outside the sensor body; alight-receiver that is incorporated in the sensor body to receivescattered light generated by the light emitted from the light-emitter tothe smoke-sensing space, and to output a light-received signalcorresponding to an amount of received light scattered; and a firejudging unit that judges presence/absence of fire occurrence based onthe amount of received light identified by the light-received signaloutput from the light-receiver.
 2. The light scattering type smokesensor according to claim 1, wherein the fire judging unit judges thepresent/absence of the fire occurrence based on the amount of receivedlight and a differential value of the amount of received light.
 3. Thelight scattering type smoke sensor according to claim 2, wherein thefire judging unit judges that fire occurs when the amount of receivedlight exceeds a predetermined fire threshold and the differential valueof the amount of received light is equal to or lower than apredetermined false alarm threshold.
 4. The light scattering type smokesensor according to claim 3, wherein when the amount of received lightexceeds the predetermined fire threshold, and the differential value ofthe amount of received light exceeds the predetermined false alarmthreshold, the fire judging unit checks whether the amount of receivedlight exceeds a predetermined obstacle threshold or not when apredetermined time elapses since the time the differential value exceedsthe predetermined false alarm threshold, and judges that there is anobstacle for fire sensing when the amount of received light exceeds theobstacle threshold.
 5. The light scattering type smoke sensor accordingto claim 1, wherein the fire judging unit judges that fire occurs, whenthe amount of received light exceeds a predetermined first firethreshold for a time equal to or longer than a predetermined first settime, and the amount of received light exceeds a predetermined secondfire threshold which is higher than the first fire threshold for a timeequal to or longer than a predetermined second set time which is longerthan the first set time.
 6. The light scattering type smoke sensoraccording to claim 1, wherein the light-emitter comprises a plurality oflight-emitters.
 7. The light scattering type smoke sensor according toclaim 6, wherein: the light-emitter comprises a first light-emitter thatemits light of a first wavelength, and a second light-emitter that emitslight of a second wavelength which is shorter than the first wavelength;and a first scattering angle formed by mutual crossing of a light axisof the first light-emitter and a light axis of the light-receivingelement is smaller than a second scattering angle formed by mutualcrossing of a light axis of the second light-emitter and the light axisof the light-receiving element.
 8. The light scattering type smokesensor according to claim 7, wherein: a central wavelength of the firstwavelength is equal to or longer than 800 nm; a central wavelength ofthe second wavelength is equal to or shorter than 500 nm; the firstscattering angle falls within a range of approximately 20° to 50°; andthe second scattering angle falls within a range of approximately 100°to 150°.
 9. The light scattering type smoke sensor according to claim 6,wherein: the light-emitter comprises a first light-emitter and a secondlight-emitter; the first light-emitter emits light having a polarizationplane vertical to a first scattering plane that passes through a lightaxis of the first light-emitter and a light axis of the light-receivingelement; the second light-emitter emits light having a polarizationplane parallel to a second scattering plane that passes through a lightaxis of the second light-emitter and the light axis of thelight-receiving element; and a first scattering angle formed by mutualcrossing of the light axis of the first light-emitter and the light axisof the light-receiving element is smaller than a second scattering angleformed by mutual crossing of the light axis of the second light-emitterand the light axis of the light-receiving element.
 10. The lightscattering type smoke sensor according to claim 9, wherein: the firstscattering angle is equal to or smaller than 80°; and the secondscattering angle is equal to or larger than 100°.
 11. The lightscattering type smoke sensor according to claim 6, wherein the plurallight-emitters are arranged at solid angles, so that planes includingrespective light axes of the plural light-emitters and the light axis ofthe light-receiving element are substantially not identical with eachother.
 12. The light scattering type smoke sensor according to claim 6,wherein: the light-emitter includes a first light-emitter and a secondlight-emitter; and the fire judging unit compares an amount of receivedlight by the light-receiver with respect to scattered light generatedfrom the light emitted by the first light-emitter and scattered by smokewith an amount of received light by the light-receiver with respect toscattered light generated from the light emitted by the secondlight-emitter and scattered by the smoke, to identify a type of thesmoke, and judges the presence/absence of fire occurrence based on astandard corresponding to the type of the smoke.
 13. The lightscattering type smoke sensor according to claim 1, wherein a mutualcrossing point of the light axis of the light-emitter and the light axisof the light-receiver in the smoke-sensing space is at leastapproximately 5 mm away from the sensor body.
 14. The light scatteringtype smoke sensor according to claim 1, wherein at least one portion ofan outer surface of the sensor body is configured by an insect avoidingmaterial, or an insect avoiding agent is applied or made to permeate toat least one portion of the outer surface of the sensor body.
 15. Thelight scattering type smoke sensor according to claim 1, wherein thelight-receiver has an angle of field of view not larger than 5 degrees.16. The light scattering type smoke sensor according to claim 1, whereinthe light-emitter emits collimated parallel beam.
 17. The lightscattering type smoke sensor according to claim 1, further comprising alogarithmic amplifier which amplifies the light-received signal outputfrom the light-receiver.
 18. The light scattering type smoke sensoraccording to claim 1, further comprising. a light emission controllerthat drives the light-emitter to intermittently emit light by using amodulated light-emission signal; and an amplifier that amplifies thelight-received signal output from the light-receiver in synchronizationwith the modulated light-emission signal.
 19. The light scattering typesmoke sensor according to claim 18, further comprising a light emissioncontroller that drives the light-emitter to intermittently emit light byusing a modulated light-emission signal, wherein: the light-emitteremits light within a visible light wavelength band; and the lightemission controller drives to intermittently emit light at alight-emission pulse width of equal to or smaller than 1 millisecond.20. The light scattering type smoke sensor according to claim 19,wherein the light emission controller sets a total light emission timeperiod in an intermittent light emission equal to or smaller than 1millisecond.